Introduction to Java
Chapter 1
Chapter 1
2
History of Java
• Java
– Originally for _______________ consumerelectronic devices
– Then used for creating Web pages with
_______________
– Now also used to:
• Develop large-scale enterprise applications
• Enhance WWW ___________ functionality
• Provide applications for consumer devices (cell
phones, etc.)
3
Java Class Libraries
• Classes
– Include methods that ________________
• Return information after task completion
– Used to build Java programs
• Java provides class ________________
– Known as Java APIs
(A_______________
P________________
I ________________
4
FORTRAN, COBOL, Pascal and Ada
• ___________________
– FORmula TRANslator
• COBOL
– COmmon ______________ Oriented Language
• Pascal
– ______________ programming
• Ada
– Multitasking
5
BASIC, Visual Basic, Visual C++, C# and
.NET
• BASIC
– Beginner’s All-Purpose ___________ ________ Code
• .NET
– .NET platform
• Visual Basic .NET
– Based on BASIC
• _______________ C++
– Based on C++
• C#
– Based on C++ and ___________________
6
Typical Java Development Environment
• Java programs normally undergo five phases
– Edit
• Programmer __________ program (and stores program on
disk)
– Compile
• Compiler creates bytecodes from program
– __________________
• Class loader stores bytecodes in memory
– Verify
• _______________ Verifier confirms bytecodes do not violate
security restrictions
– Execute
• JVM translates bytecodes into machine language
7
Fig. 1.1 Typical Java
development
environment.
8
Creating a Program with JCreator
• Click on the JCreator ____________
• IDE
window
appears
9
Creating a Program with JCreator
• Click on File, New, then P______________
• Project Wizard appears
– Choose Java ________________ template
10
Creating a Program with JCreator
• Give the project a _________________
• Then click Next
11
Creating a Program with JCreator
• You will want the JDK version 1.5
At this point you can click on Finish
12
Creating a Program with JCreator
• Now we create our class (the program) with
File, New, and Class
13
Creating a Program with JCreator
• The wizard creates a __________________.
• Now complete the program with the
required commands.
14
Creating a Program with JCreator
• Run the compiler with Build, and
CompileFile
___________________ shows in bottom pane. This is
where compiler error messages will be displayed.
15
Creating a Program with JCreator
• To run the compiled program click on Build,
and _________________
• Program runs in separate window
Introduction
to Java Applications
Chapter 2
16
17
2.1 Introduction
• Java application programming
–
–
–
–
Display ___________________________
Obtain information from the user
____________________ calculations
Decision-making fundamentals
18
2.2 First Program in Java: Printing a Line
of Text
• Application
– Executes when you use the java command to
launch the J_______V_______ M________
Sample program
– Displays a line of text
– Illustrates several important Java language
features
19
2.2 First Program in Java: Printing a Line
of Text (Cont.)
1
// Fig. 2.1: Welcome1.java
– Comments start with: ____________
• Comments ignored during program execution
• Document and describe code
• Provides code readability
– Traditional comments: ________________
/* This is a traditional
comment. It can be
split over many lines */
2
// Text-printing program.
– Another line of comments
– Note: line numbers not part of program, added for
reference
20
2.2 First Program in Java: Printing a Line
of Text (Cont.)
3
– Blank line
• Makes program more __________________
• Blank lines, spaces, and tabs are white-space characters
– _______________________ by compiler
4
public class Welcome1
– Begins class declaration for class Welcome1
• Every Java program has at least one ________________
• Keyword: words reserved for use by Java
– class keyword followed by class name
• Naming classes: ______________________________
– SampleClassName
21
2.2 First Program in Java: Printing a Line
of Text (Cont.)
4
public class Welcome1
– Java identifier
• Series of characters consisting of letters, digits,
underscores ( _ ) and dollar signs ( $ )
• Does not begin with a ____________, has no _______
• Examples: Welcome1, $value, _value, button7
– 7button is invalid
• Java is case sensitive (capitalization matters)
– a1 and A1 are different
– In chapters 2 to 7, use public class
• Certain details not important now
• Mimic certain features, discussions later
22
2.2 First Program in Java: Printing a Line
of Text (Cont.)
4
public class Welcome1
– Saving files
• File name must be class name with ._______ extension
• Welcome1.java
5
{
– Left brace {
• Begins _________________ of every class
• Right brace ends declarations (line 13)
23
2.2 First Program in Java: Printing a Line
of Text (Cont.)
7
public static void main( String args[] )
– Part of every Java application
• Applications begin executing at main
– Parentheses indicate main is a ______________ (Ch. 3 and 6)
– Java applications contain one or more methods
• Exactly one method must be called _________________
– Methods can perform tasks and return information
• ______________ means main returns no information
• For now, mimic main's first line
8
{
– Left brace begins body of method declaration
• Ended by right brace } (line 11)
24
2.2 First Program in Java: Printing a Line
of Text (Cont.)
9
System.out.println( "Welcome to Java Programming!" );
– Instructs computer to perform an action
• Prints string of characters
– String - series characters inside ___________ quotes
• White-spaces __________ are not ignored by compiler
– System.out
• Standard output object
• Print to command window (i.e., MS-DOS prompt)
– Method System.out.println
• Displays line of text
– This line known as a statement
• Statements must end with __________________
25
2.2 First Program in Java: Printing a Line
of Text (Cont.)
11
} // end method main
– Ends method declaration
13
} // end class Welcome1
– Ends class declaration
– Can add __________________ to keep track of
ending braces
26
2.3 Modifying Our First Java Program
• Modifying programs
– Welcome2.java (Fig. 2.3) produces same output as
Welcome1.java (Fig. 2.1)
– Using different code
9
10
System.out.print( "Welcome to " );
System.out.println( "Java Programming!" );
– Line 9 displays “Welcome to ” with cursor remaining on
printed line
– Line 10 displays “Java Programming! ” _____________ with
cursor on next line
27
2.3 Modifying Our First Java Program
(Cont.)
• Escape characters
– Backslash ( \ )
– Indicates _____________________ be output
• ____________________ characters (\n)
– Interpreted as “special characters” by methods
System.out.print and System.out.println
– Indicates cursor should be at the beginning of the next line
– Welcome3.java (Fig. 2.4)
9
System.out.println( "Welcome\nto\nJava\nProgramming!" );
– Line breaks at \n
28
Escape Description
sequence
\n
Newline. Position the screen cursor at the beginning of the next line.
\t
\r
Horizontal tab. Move the screen cursor to the next tab stop.
Carriage return. Position the screen cursor at the beginning of the
current line—do not advance to the next line. Any characters output
after the carriage return overwrite the characters previously output
on that line.
Backslash. Used to print a backslash character.
Double quote. Used to print a double-quote character. For example,
System.out.println( "\"in quotes\"" );
displays
"in quotes"
\\
\"
Fig. 2.5 | Some common escape sequences.
29
2.4 Displaying Text with printf
•System.out.printf
– New feature of J2SE 5.0
– Displays _________________ data
9
10
System.out.printf( "%s\n%s\n",
"Welcome to", "Java Programming!" );
– Format string
• Fixed text
• Format ____________ – placeholder for a value
– Format specifier %s – placeholder for a _______
– Other format specifiers
30
Formatting Output with printf
•printf
– Precise output formatting
• Conversion specifications: flags, field widths, precisions, etc.
– Can perform
•
•
•
•
•
•
•
•
_________________________
aligning columns
right/left _______________________
inserting literal characters
exponential format
octal and hexadecimal format
fixed width and ____________________
date and time format
31
Formatting Output with printf (Cont.)
• Format String
– Describe the output format
– Consist of fixed text and format specifier
• Format specifier
– Placeholder for a value
– Specify the ________________ of data to output
– Begins with a ________________ and is followed by a
conversion character
• E.g., %s, %d
– Optional formatting information
• Argument index, flags, field width, precision
• Specified between % and conversion character
32
Printing Integers
• Integer
– Whole number (no decimal point): 25, 0, -9
– Positive, negative, or zero
– Only __________________ prints by default (later we shall
change this)
• Format
– printf( format-string, argument-list );
– format-string
• Describe the output format
– argument-list
• Contain the ____________ corresponding to each format
specifier
33
Integer conversion characters.
Conversion character
Description
d
Display a decimal (base 10) integer.
o
Display an octal (base 8) integer.
x or X
Display a hexadecimal (base 16) integer. X causes the digits 0–9
and the letters A–F to be displayed and x causes the digits 0–9
and a–f to be displayed.
• View demonstration program Fig. 28.3
– Note output of positive, negative numbers
– Note octal (base 8) and hexadecimal (base 16) options
34
Printing Floating-Point Numbers
• Floating Point Numbers
– Have a ______________ point (33.5)
– Computerized scientific notation (exponential
notation)
• 150.4582 is 1.504582 x 10² in scientific
• 150.4582 is 1.504582e+02 in exponential (e stands for
exponent)
• use e or E
– f – print _________________ with at least one digit
to left of decimal
– g (or G) - prints in f or e (E)
• Use exponential if the magnitude is less than 10-3, or
greater than or equal to 107
35
Floating-point conversion characters.
Conversion character
Description
e or E
Display a floating-point value in exponential notation. When
conversion character E is used, the output is displayed in
uppercase letters.
F
Display a floating-point value in decimal format.
g or G
Display a floating-point value in either the floating-point
format f or the exponential format e based on the magnitude
of the value. If the magnitude is less than 10–3, or greater than
or equal to 107, the floating-point value is printed with e (or
E). Otherwise, the value is printed in format f. When
conversion character G is used, the output is displayed in
uppercase letters.
a or A
Display a floating-point number in hexadecimal format.
When conversion character A is used, the output is displayed
in uppercase letters.
• View program using printf for floating point
numbers, Figure 28.4
36
Printing Strings and Characters
• Conversion character c and C
– Require ________________
– C displays the output in uppercase letters
• Conversion character s and S
– String
– Object
• Implicitly use object’s _______________ method
– S displays the output in uppercase letters
• View program demonstrating character conversion
with printf, Fig. 28.5
37
Printing with Field Widths and Precisions
• Field width
– Size of field in which data is printed
– If width larger than data, default __________ justified
• If field width too small, ______________ to fit data
• Minus sign uses one character position in field
– Integer width inserted between % and conversion specifier
• E.g., %4d – field width of 4
– Can be used with all format specifiers except the _________
separator (%n)
• View program demonstrating field width,
Fig. 28.12
38
Printing with Field Widths and Precisions
• Precision
– Meaning varies depending on data type
– Floating point
• Number of digits to appear ____________ decimal
(e or E and f)
• Maximum number of significant digits (g or G)
– Strings
• ____________ number of characters to be written from string
– Format
• Use a dot (.) then precision number after %
e.g., %.3f
• View program demonstrating precision,
Fig. 28.13
39
Printing with Field Widths and Precisions
• Field width and precision
– Can both be specified
• %width.precision
%5.3f
– ________________ field width – left justified
– Positive field width – right justified
– Precision must be _________________
• Example:
printf( "%9.3f", 123.456789 );
40
2.5 Another Java Application: Adding
Integers
• Program Fig. 2.7 to do keyboard input
– Use ___________ to read two integers from user
– Use printf to display sum of the two values
– Use packages
41
2.5 Another Java Application: Adding
Integers (Cont.)
3
import java.util.Scanner;
// program uses class Scanner
– import declarations
• Used by _________________ to identify and locate classes used
in Java programs
• Tells compiler to load class Scanner from java.util package
5
6
public class Addition
{
– Begins public class Addition
• Recall that file name must be Addition.____________
– Lines 8-9: begins main
42
2.5 Another Java Application: Adding
Integers (Cont.)
10
11
// create Scanner to obtain input from command window
Scanner input = new Scanner( System.in );
– Variable Declaration Statement
– Variables
• Location in memory that stores a _____________
– Declare with name and type before use
• Input is of type Scanner
– Enables a program to read data for use
• Variable name: any valid identifier
– Declarations end with semicolons ;
– Initialize variable in its ________________
• Equal sign
• Standard input object
– System.in
43
2.5 Another Java Application: Adding
Integers (Cont.)
13
14
15
int number1; // first number to add
int number2; // second number to add
int sum; // second number to add
– Declare variable number1, number2 and sum of type
int
• int holds integer values (whole numbers): i.e., 0, -4, 97
• Types ___________ and double can hold decimal numbers
• Type char can hold a __________ character: i.e., x, $, \n, 7
• int, float, double and char are _____________ types
– Can add comments to describe purpose of variables
int number1, // first number to add
number2, // second number to add
sum; // second number to add
– Can declare ______________ variables of the same
type in one declaration
– Use comma-separated list
44
2.5 Another Java Application: Adding
Integers (Cont.)
17
System.out.print( "Enter first integer: " ); // prompt
– Message called a ____________ - directs user to
perform an action
– Package java.lang
18
number1 = input.nextInt(); // read first number from user
– Result of call to nextInt given to number1 using
assignment operator =
• Assignment statement
• = binary operator - takes ____________ operands
– Expression on right evaluated and assigned to variable
on left
• Read as: number1 __________________ input.nextInt()
45
2.5 Another Java Application: Adding
Integers (Cont.)
20
System.out.print( "Enter second integer: " ); // prompt
– Similar to previous statement
• Prompts the user to input the second integer
21
number2 = input.nextInt(); // read second number from user
– Similar to previous statement
• Assign variable number2 to second integer input
23
sum = number1 + number2; // add numbers
– Assignment statement
• ___________ of number1 and number2 (right hand side)
• Uses assignment operator = to assign result to variable sum
• Read as: sum gets the value of number1 + number2
• number1 and number2 are _________________
46
2.5 Another Java Application: Adding
Integers (Cont.)
25
System.out.printf( "Sum is %d\n: " , sum ); // display sum
– Use System.out.printf to display results
– _______________ specifier %d
• Placeholder for an int value
System.out.printf( "Sum is %d\n: " , ( number1 + number2 ) );
– Calculations can also be performed inside
_______________
– Parentheses around the expression number1 +
number2 are not required
47
2.6 Memory Concepts
• Variables
– Every variable has a name, a ___________, a
_______________ and a value
• Name corresponds to location in memory
– When new value is placed into a variable, replaces
(and ______________) previous value
– ________________ variables from memory does not
change them
48
2.7 Arithmetic
• Arithmetic calculations used in most
programs
– Usage
• * for multiplication
• / for division
• % for ___________________
• +, -
– Integer division _____________ remainder
7 / 5 evaluates to 1
– Remainder operator % returns the remainder
7 % 5 evaluates to 2
49
Java
operation
Arithmetic Algebraic
operator
expression
Java
expression
Addition
+
f+7
f + 7
Subtraction
–
p–c
p - c
Bm
b * m
Multiplication *
Division
/
x / y or
or x ÷ y
Fig. 2.11 | Arithmetic operators.
x / y
50
2.7 Arithmetic (Cont.)
• Operator precedence
– Some arithmetic operators act before others (i.e.,
multiplication before addition)
• Use ___________________ when needed
– Example: Find the average of three variables a, b
and c
• Do not use: a + b + c / 3
• Use: ( a + b + c ) / 3
51
Operator(s) Operation(s) Order of evaluation
(precedence)
*
Multiplication
/
Division
%
Remainder
+
Addition
-
Subtraction
Evaluated first. If there are
several operators of this type,
they are evaluated from left to
right.
Evaluated next. If there are
several operators of this type,
they are evaluated from left to
right.
Fig. 2.12 | Precedence of arithmetic operators.
52
Operator Precedence Chart
Hierarchy of Java operators with the highest precedence shown first.
• Expressions inside parentheses are evaluated first; nested parentheses are evaluated from the
innermost parentheses to the outer.
• Operators in the same row in the chart have equal precedence.
Operator
Type
Order of
Evaluation
( )
[ ]
.
Parentheses
Array subscript
Member access
left to right
Prefix increment,
decrement
right to left
Postfix increment,
decrement
Unary minus
right to left
Multiplicative
left to right
Additive
left to right
Relational
left to right
Equality
left to right
&&
And
left to right
||
Or
left to right
++
--
++
--
*
/
+
-
<
>
==
-
%
<=
>=
!=
?
:
Conditional
right to left
=
=
+= *= /=
Assignment
right to left
%=
53
View Flash Presentations
• Creating a workspace, project, and
application
• Writing, compiling, running an application
3
• Introduction to Classes and Objects
55
3.2 Classes, Objects, Methods and
Instance Variables
• Class provides one or more ______________
• Method represents task in a program
– Describes the _____________ that actually perform
its tasks
– Hides from its user the complex tasks that it
performs
– Method _____________ tells method to perform its
task
• Classes contain one or more attributes
– Specified by instance variables
– Carried with the object as it is used
56
3.3 Declaring a Class with a Method and
Instantiating an Object of a Class
• Each class declaration that begins with
keyword public
– must be stored in a _______________
– that has the same ___________ as the class
and
– ends with the .__________ file-name
extension.
57
Class GradeBook
• keyword public is an ___________ modifier
• Class declarations include:
– Access modifier
– Keyword class
– Pair of left and right braces
• Method declarations
– Keyword ____________ indicates method is
available to public
– Keyword void indicates _______________
– Access modifier, return type, name of method and
parentheses comprise method header
58
Class GradeBookTest
• Java is ______________________
– Programmers can create new classes
– Test program
the GradeBook class
• Class instance creation expression
– Keyword _____________
– Then name of class to create and parentheses
• Calling a method
– Object _______________, then dot separator (.)
– Then method name and parentheses
59
Compiling an Application with Multiple
Classes
• Note we have two classes
– Gradebook
– GradeBookTest
• Compiling multiple classes
– Use the compile command in the IDE
– Compile each file ___________ (or use
Compile Project command)
• Requires a ____________ in some IDE’s
60
3.4 Declaring a Method with a Parameter
• Method ___________________
– Additional information passed to a method
– Supplied in the method call with _________
•Scanner methods
– _______________ reads next line of input
– next reads next ___________ of input
• See new improved GradeBook class, Figure
3.4 and GradeBookTest program, Figure 3.5
61
Outline
1
// Fig. 3.4: GradeBook.java
2
GradeBook.java
// Class declaration with a method that has a parameter.
3
4
public class GradeBook
5
{
6
// display a welcome message to the GradeBook user
7
public void displayMessage( String courseName )
8
{
9
10
11
System.out.printf( "Welcome to the grade book for\n%s!\n",
courseName );
} // end method displayMessage
12
13 } // end class GradeBook
62
Notes on Import Declarations
•__________________ is implicitly imported into
every program
• Default package
– Contains classes compiled in the ________________
– Implicitly imported into source code of other files in
directory
• Packages unnecessary if fully-qualified names are
used
63
3.5 Instance Variables, set Methods and
get Methods
• Variables declared in the body of method
– Called _______________ variables
– Can only be used within that method
• Variables declared in a class declaration
– Called fields or _______________ variables
– Each object of the class has a separate instance of the
variable
• Note set and get methods
64
Access Modifiers public and private
• private keyword
– Used for most instance variables
– private variables and methods are accessible
only to methods of the
____________________________________
– Declaring instance variables private is known
as data ____________________
• Return type
– Indicates item returned by method
– Declared in method header
GradeBookTest Class That
Demonstrates Class GradeBook
• Default initial value
– Provided for all fields not initialized
– Equal to _____________ for Strings
• Note
private instance variables
– Cannot be accessed directly by ____________ of the
object
– Use set methods to ____________ the value
– Use ______________ methods to retrieve the value
65
66
Primitive Types vs. Reference Types
• Types in Java
– Primitive
•boolean, byte, char, short, _______,
long, float, _______________
– Reference (sometimes called ____________
types)
• Objects
• Default value of null
• Used to invoke an object’s methods
67
3.7 Initializing Objects with Constructors
• Constructors
– _____________ an object of a class
– Java requires a constructor for every class
– Java will provide a default no-argument
constructor if none is provided
• Called when keyword _________ is
followed by the class name and parentheses
• Constructors which
“incoming”
initial value
AccountTest Class to use Class
Account
• Note use of Scanner object
– Input floating point number
• Note use of ____________________ %f
– Used to output floating-point numbers
– Place a decimal and a number between the percent
sign and the f to mandate a ________________
68
69
Displaying Text in a Dialog Box
• Windows and dialog boxes
– Many Java applications use these to display
output
– ________________ provides prepackaged
dialog boxes called message dialogs
• Program to use dialog box
70
Displaying Text in a Dialog Box
• Package javax.swing
– Contains classes to help create
_______________________________ (GUIs)
– Contains class JOptionPane
• Declares static method showMessageDialog for displaying
a message dialog
71
Entering Text in a Dialog Box
• Input dialog
– Allows user to input information
– Created using method
_____________________ from class
JOptionPane
Methods
Chapter 6
72
Program Modules in Java
• What we call "functions" in C++ are called
"________________" in Java
• Purpose
– Reuse code
– ______________________ the program
• This can be done by putting the code in a
method
– Various objects in a program can invoke the same
method
73
Program Modules
• _______________ and ______________
technique
– Construct a large program from smaller pieces (or
modules)
– Can be accomplished using methods
• ______________ methods can be called
without the need for an object of the class
74
static Methods
•static method (or class method)
– Applies to the class as a whole instead of a specific
object of the class
– Call a static method by using the method call:
_____________.methodName( arguments )
– All methods of the __________ class are
static
• example: Math.sqrt(
900.0 )
75
static Methods
• Method main
– main is declared static so it can be invoked
_____________________________ of the class
containing main
– Any class can contain a main method
– The JVM invokes the main method belonging to
the class specified by the first command-line
argument to the java command
76
Predefined Methods
• The Math class
• These methods are called by
– The _____________ of the class
– The dot . operator
– The name of the ______________
• Example:
double y = Math.cos(x);
77
Constants
• Constants
– Keyword ___________________
– Cannot be changed after initialization
• static fields (or class variables)
– Are fields where one copy of the variable is
__________________ among all objects of the
class
• Math.PI and Math.E are final static
fields of the Math class
78
Method Declaration Syntax
modifiers returnType methodName
(parameterDeclaration)
{
statements
}
• ___________ : describers (public, private, etc.)
• returnType : type of value returned by method, or
____________ if it does not return a value
• methodName : identifier that names the method
• parameterDeclaration : list of parameters, separated
by _______________________
79
• statements : define the behavior of the method
Method Declaration
• View declaration of methods in a class for
finding maximums, Fig. 6.3
– Note method for input, call of method
______________
– Note method for actual determining of maximum
• View test program, Fig 6.4
– Note declaration of instance of new class
– Note call of class methods
80
Alternative Method Declaration
• View alternative solution
• Declare methods in the __________________
• Have them follow method main()
– Although they can be ____________ in the class
• Note they must be static
81
Declaring and Using Methods
• Three ways to call a method:
– Use a method name by itself to call ____________
of the same class
– Use a
containing a reference to an object,
followed by a dot (.) and the method name to call a
method of the referenced object
– Use the class name and a dot (.) to call a _______
method of a class
– Note: static methods cannot call non-static
methods of the same class directly
82
Declaring and Using Methods
• Three ways to return control to the calling
statement:
– If method does not return a result:
• Program flow reaches the _________________ right
brace or …
• Program executes the statement _____________;
– If method does return a result:
• Program executes the statement
__________ expression;
• expression is first evaluated and then its value is returned
to the caller
83
Argument Promotion
• Coercion of arguments
– _______________ arguments to appropriate type
to pass to method
System.out.println( Math.sqrt( 4 ) );
– Evaluates Math.sqrt( 4 )
– Then evaluates System.out.println()
84
Argument Promotion
• Promotion rules
– Specify how to convert types without data
loss
Type
Valid promotions
double
float
long
int
char
short
byte
boolean
None
double
float or double
long, float or double
int, long, float or double
int, long, float or double (but not char)
short, int, long, float or double (but not char)
None (boolean values are not considered to be numbers in Java)
85
Java API Packages
• _______________ classes grouped into
categories of related classes
– Called packages
• Called the Java Application Programming
Interface (API)
• Note the often used API packages
86
Random-Number Generation
• Consider the random method in the Math
class
– Generates a random double 0 <= n < ______
– The number can be manipulated and cast as an
______ to get desired range
– For the roll of a die
1 + (int) (Math.random() * 6)
• Note Figure 6.7 and Figure 6.8
87
Game of Chance
Rules for "Craps"
• Roll dice first time
– If sum equals 7 or 11, the player _________
– If sum equals ____________, the player loses
– Any other sum (4, 5, 6, 8, 9, 10) is that player’s
point
• Keep rolling dice until…
– Sum matches player point
• Player wins
– Sum equals _______
• Player loses
88
Game of Chance
• Note the adapted version of Figure 6.9
– An application
• Note
– _____________ class variables
– Public methods
– The __________________ function requires
Character. (a non instantiating class)
89
Scope of Declarations
• Scope of a ______________ is body of method where
declaration appears
• Scope of local variable is from point of declaration to
end of ________________
• Scope of label in labeled break/continue is statement
enclosed by labeled statement
• Scope of local-variable in initialization of for( ) is for
_______________________ and rest of header
• Scope of method or field of class is body of
____________
90
Shadowing
• A field is shadowed (or hidden) if a
_____________ variable or parameter has the
same name as the field
• This lasts until the local variable or parameter
goes out of ______________
• View example
– Figure 6.11
– Figure 6.12
Variables with different scopes
Test program
91
Method Overloading
• Multiple methods with _____________ can be
declared in same class
• Methods must have different ___________
– Different numbers, types, order of parameters
• Example
– Figure 6.13 Overload example class
– Figure 6.14 Overload test program
92
Recursion
Recursive method
• Calls ___________ (directly or indirectly)
through another method
• Method knows how to solve only a ______ case
• Method divides problem
– Base case
– Simpler problem – Method now divides simpler
problem until solvable
• Recursive call
• Recursive step
93
Recursive Evaluation of 5!
Final value = 120
5!
5!
5! = 5 * 24 = 120 is returned
5 * 4!
5 * 4!
2! = 2 * 1 = 2 is returned
4! = 4 * 6 = 24 is returned
4 * 3!
4 * 3!
3! = 3 * 2 = 6 is returned
3 * 2!
3 * 2!
2 * 1!
2 * 1!
1 returned
1
(a) Sequence of
recursive calls.
1
(b) Values returned
from each
recursive call.
94
Recursive Factorial Program
• Function factorial() in Figure 6.15
• Note
– Initial call to factorial()
– ____________ or base case
– Recursive call
95
Recursive Fibonacci Program
• Consider function from program
public long fibonacci( long n )
{
// base case
if ( n == 0 || n == 1 )
return n;
// recursive step
else
return fibonacci( n - 1 ) + fibonacci( n - 2 );
} // end method fibonacci
• Note why this would be extremely _________
96
Recursive Fibonacci Program
fibonacci( 3 )
return
return
fibonacci( 1 )
return 1
fibonacci( 2 )
+
fibonacci( 0 )
+
fibonacci( 1 )
return 1
return 0
97
Recursion vs. Iteration
• Both the recursive functions shown can be
done with either for or while loops
• In fact they are done more efficiently
____________
• Recursion has overhead
– Processor time
– Memory space
• General rule: If it can be done either
recursively or iteratively … choose __________
98
Arrays
Chapter 7
99
Declaring and Creating Arrays
• Recall that an array is a collection of elements
all of the _____________
• Array objects in Java must be created with the
key word _______________
• Syntax
int c[] = new int [12];
• Results:
– 12 integer locations are allocated
– They are _____________________
(null for reference variables, false for boolean)
100
Using Arrays
• View example Figure 7.2
• Note
– Declaration of the array
– Allocation of memory with new
– Initialization of array elements
– Use of array attribute (_______________)
– Printing of array contents
101
The Array Initializer
• A comma separated list of expressions
– The ______________ list
– Enclosed in _________________
• View the Example
– Note again, how the array knows its own _______
for (int count = 0 ; count < array.length ; count++)
. . .
102
Processing Elements of An
Array
• Finding and using the arithmetic mean
– __________________ the array, create
– Read in values, ___________________
– Declare a summation variable, initialize
– ______________ the array, calculate average
– _______________ the array
– Print results, accessing the array
• See sample program
103
Histogram Program
• Use the value in the array to
– Print the value
– Print a string of asterisks for __________________
of size of the value
• View Figure 7.6,
104
Using Array Elements as
Counters
• Recall program which tested random number
generator (Figure 6.8)
– Used 6 different variables
– Used switch statement to increment
– At the time we noted the ________________
• Consider a new version of the program
– Uses _______________ to total the number of rolls
of each number 1 – 6
– No ___________ statement needed
• View Figure 7.7
105
Enhanced for Statement
• Enhanced for statement
– New feature of J2SE 5.0
– Allows iterates through elements of an array or a
collection _______________________
– Syntax
for ( parameter : arrayName )
statement
– View example, Figure 7.12
106
References and Reference
Parameters
• In Java, primitive-type variables
are always passed by _________
– Incoming data only
• Objects are not passed to methods
– __________ to objects are passed
– The reference is passed by value
• With a reference to the object the method can
_____________ the object directly
107
References and Reference
Parameters
• Passing arrays by reference
– Improves _______________
– Saves time
• ________________ of large array not required
– Saves _______________
• Use memory already occupied by array
• No new memory allocation required
– View example program, Figure 7.13
108
Using Arrays
• Sorting Arrays
– Recall previous example
• Searching Arrays
– ________________ search (see example)
• Step through array until desired value located
– Binary search
• Array must be _________________
• Look in middle, then above or below
– Look in middle of sub-section then above or below
– Etc.
109
Multidimensional Arrays
• Java does not support ________________
arrays directly
• Does allow declaration of arrays whose
elements are ______________!
int b[][];
b = new int[ 2 ][ ];
// allocate rows
b[ 0 ] = new int[ 5 ]; // allocate columns for row 0
b[ 1 ] = new int[ 3 ]; // allocate columns for row 1
110
Multidimensional Arrays
Fig. 7.16 | Two-dimensional array with three
rows and four columns.
111
Creating Two-dimensional
Arrays
– Can be created dynamically
– 3-by-4 array
int b[][];
b = new int[ 3 ][ 4 ];
– Rows can have different number of ____________
int b[][];
b = new int[ 2 ][ ];
// create 2 rows
b[ 0 ] = new int[ 5 ];
// create 5 columns for row 0
b[ 1 ] = new int[ 3 ];
// create 3 columns for row
112
Variable-Length Argument Lists
• New feature in J2SE 5.0
• ___________________ number of arguments
• Use ellipsis (…) in method’s parameter list
– Can occur _______________ in parameter list
– Must be placed at the __________ of parameter list
• Array whose elements are all of the same type
• View example, Fig. 7.20
113
Using Command-Line
Arguments
• Pass arguments from the command line
– String args[]
• Appear after the _____________ in the java
command
– java MyClass a b
• _________________ of arguments passed in
from command line
– args.length
• First command-line argument
– args[ 0 ]
114
Object Based Programming
Chapter 8
115
Contrast
• ____________________ Languages
– Action oriented
– Concentrate on writing ________________
– Data supports the actions
• Object Oriented Languages
– Concentrate on creating reference types
– Look for ____________ which indicate classes
• Fields are data members
• Methods support manipulation of the objects
116
Find the Objects … the Verbs
What are verbs that
represent things that the
objects do?
In this game, what
are nouns that are
potential classes?
117
Abstract Data Types (ADTs)
• Classes in Java make creation of ADTs easier
– Implementation details ____________ from users
of the class
– Client code not dependent on ________________
• Example of a class
– Figure 8.1
– Time class – keeps track of time in 24 hour format
118
Declaring Classes
• Usually data fields are specified as __________
• ______________ are declared as public
• Any class member (data or method) which does
not need to be accessed outside the class
should be private
• It ____________________________ which
comes first, data fields or methods
– The author prefers data fields first
119
Constructors
• Methods which have the same name as the
_____________________
• Included in a class to ensure that instance
variables contain __________________ when
objects are created
• The constructor is called when a class object is
created with the __________________
• Note:
– Do not have the constructor return a _________
120
Using Classes
• View Figure 8.2
• Note
– Creation of a time object with new
– Call of the constructor
– Use of public functions to ____________ the private data
values
– Use of toString functions
– Use of DecimalFormat class
• Advantages of classes
– Simplifies client __________________ of classes
– Reduces number of _______________________
121
Class Scope
• Variables and methods belong to the class's
scope
• _________________ the class's scope
– All class members are available, accessible
• Outside the class's scope
– Client code that uses the class
– Only _____________ members are available,
accessible
• Access modifiers public and private control this
122
availability
Controlling Access to Members
• The following would not be allowed – why?
public class TimeTest2 {
public static void main( String args[] )
{
Time1 t = new Time1();
t.hour = 7;
}
}
• The data members are ___________.
123
Using the this Reference
• Every object can access a reference to ______
– Use the keyword this
• If a method has a ________ variable with same
name as _________ variable, use the this to
access the class variable
• Explicit use of this can increase program
_____________ for human readers
• Note example, Figure 8.4
124
Using Overloaded Constructors
• ________________ constructors for the same
class are allowed
• The _____________ of the constructors must
be different
– Different numbers and/or types of parameters
• See example in Figure 8.5 and 8.6
125
Using Set and Get Methods
• Private data fields manipulated only by provided
_________________________
– Some methods used to _________ the data values
– Others used to get the values
• Return the value directly
• Print the value
• Note: this is not the same as making the data
values __________________
– The set methods are written to ensure valid data
values
126
Composition
• A class can have references to
__________________________ as members
• Example:
– An alarm clock class contains a Time object as one
of its members
– Employee class has Date object as one of its
members
– See
• Date Class, Figure 8.7
• Employee Class Figure 8.8
• Employee Test program Figure 8.9
127
Enumerations – enum types
• Declared with an ___________ declaration
• A comma-separated list of enum constants
• Declares an enum class with the following
restrictions:
– enum types are implicitly _____________
– enum constants are implicitly ______________
– Attempting to create an object of an enum type with
new is a compilation error
128
Enumerations – enum types
constants can be used anywhere
_____________ can
• enum constructor
• enum
– Like class constructors, can specify
____________ and be overloaded
• See example, Figure 8.10
• Note test program, Figure 8.11
129
Enumerations – enum types
•static method values
– Generated by the __________ for every enum
– Returns an array of the enum’s constants in the
order in which they were declared
•static method _________ of class EnumSet
– Takes two parameters, the first and last enum
constants in the desired range
– Returns an EnumSet containing the constants in
that range, ________________
– An enhanced _________ statement can iterate
over an EnumSet as it can over an array
130
Garbage Collection
• Garbage collection
– JVM marks an object for garbage collection when there are
no more _________________ to that object
– JVM’s garbage collector will retrieve those objects memory
so it can be used for other objects
– See lines 27 – 32 of Figure 8.13
• _________________ method
– All classes in Java have the finalize method
• Inherited from the Object class
– finalize is called by the ____________________ when it
performs termination housekeeping
– finalize takes no parameters and has no return type
131
_____________
static Class Members
• Normally each class object has its own copy of the
instance variables
• Possible to specify a variable that is __________ by
all existing objects of the class
– Called a static variable
– Also called a __________ variable – class wide information
• Also possible to have a static ______________
– Can be called even if no object of the class has been
instantiated
– Use class name, then dot, then static method name
• Note examples in Fig. 8.12, test pgm Fig. 8.13
132
static Class Members
•String objects are _________________
– String concatenation operations actually result in
the creation of a ___________ String object
•static methods ________________ nonstatic class members
– Also cannot use the ____________ reference
133
static Class Members
• static method _________ of class System
– Indicates that the garbage collector should make a
best-effort attempt to reclaim objects eligible for
garbage collection
– It is possible that _______ objects or only a
_________ of eligible objects will be collected
• Note example call in Fig. 8.13
134
static Import
• Recall static fields and methods of class Math
• J2SE 5.0 enables importing static members as
if ______________________ where used
• Note Figure 8.14
import static java.lang.Math.*
135
Final Instance Variables
• Principle of least privilege
– Code should have only the privilege and access it
needs to ________________, but no more
• final instance variables
– Keyword ______________
• Specifies that a variable is ______ modifiable (is a
constant)
– final instance variables can be initialized at their
_______________________
• If they are not initialized in their declarations, they must
136
be initialized in all constructors – Fig. 8.15
Software Reusability
• Many classes exist in the Java API
• Avoid "__________________"
– Study capabilities of Java API
– If it has a class that fits your needs, use it rather
than creating your own
137
Data Abstraction & Encapsulation
• Information hiding
– Classes hide details of _______________ from
client
• Example:
– Stack can be implemented with array or with linked
list
– Client program which depends on one
implementation will have problems if new version
with different implementation comes out
• Only use the ________________ provided
138
Object Oriented Programming:
Inheritance
Chapter 9
139
Introduction
• Software Reusability
– saves __________ in program development
– encourages use of proven, ____________ code
– reduces problems
• Write programs in ____________ fashion
• Enables software designers to deal with
complexity of modern software
140
Introduction
• When creating a new class …
– designate that class to ___________ data
members, functions of previously defined
superclass
– result is a ___________________
• Subclass ____________ new data members
and functions
• ________________ and refine existing
members
141
Base Classes & Derived
Classes
• Superclass is more ______________
– student, shape, loan
• ________________ is more specific
– grad student, undergrad
– circle, triangle, rectangle
– carloan, home improvement, mortgage
• Some languages talk of
– ______________ class (Superclass)
– Derived class (Subclass)
142
Superclass and Subclass
• Inheritance produces _________ like structures
143
Superclass and Subclass
• Inheritance produces tree like structures
144
Design Tip
• Important link between subclass and
superclass
– The “_____________” relationship
• Examples
– A checking account IS-A banking account
– A savings account IS NOT a checking account
• If there is no IS-A relationship, do not use
__________________
145
protected Members
•protected access
– ______________ level of protection between
public and private
– protected members accessible by
• superclass members
• _________________ members
• Class members in the same package
– Subclass access to superclass member
• Keyword _____________ and a dot (.)
146
Comments on Private vs. Protected
• Use protected when
– Superclass should provide a _____________ only
to its subclasses
– Should not provide service to other clients
• Use private so that
– ________________ implementation can change
without affecting subclass implementations
• Author advocates ______________ protected
– Instead provide set and get methods to access
private data items (see Figures 9.12, 9.13 in text)
147
Relationship between
Superclasses and Subclasses
• Superclass and subclass relationship
– Example: CommissionEmployee/
BasePlusCommissionEmployee inheritance
hierarchy
• CommissionEmployee
– First name, last name, SSN, commission rate, gross sale
amount
• BasePlusCommissionEmployee
– First name, last name, SSN, commission rate, gross sale
amount
– Base salary
148
Creating and Using a
CommissionEmployee Class
• Class CommissionEmployee
– Extends class Object
• ______________________ extends
• Every class in Java extends an existing class
– Except Object
• Every class inherits __________________
methods
• New class _________________ extends Object
– If it does not extend another class
149
Creating and Using a
CommissionEmployee Class
• Class CommissionEmployee
– Extends class Object
• Keyword extends
• Every class in Java extends an existing class
– Except Object
• Every class inherits Object’s methods
• New class implicitly extends Object
– If it does not extend another class
• View class Figure 9.4
• View test program, Figure 9.5
150
Creating a
BasePlusCommissionEmployee
Class without Using Inheritance
• Class BasePlusCommissionEmployee
– Implicitly extends Object
– Much of the code is similar to
CommissionEmployee
• private ____________ variables
• public methods
• constructor
– ____________
• private instance variable baseSalary
• Methods setBaseSalary and getBaseSalary
151
Creating a CommissionEmployeeBasePlusCommiionEmployee Inheritance
Hierarchy
• Class BasePlusCommissionEmployee2
– Extends class CommissionEmployee
– Is a CommissionEmployee
– Has ___________ variable baseSalary
– _____________ public and protected
members
– _______________ not inherited
• Note these points plus invalid references, Figure
152
9.8 – note compiler error messages
Using protected Instance Variables
• Use protected instance variables
– Enable class BasePlusCommissionEmployee to
__________________ superclass instance
variables
– Superclass’s protected members are inherited by
all subclases of that superclass
• View version that now works, Figure 9.10
• Test program, Figure 9.11
153
Using protected Instance Variables
Advantages
• Subclasses can _________________ values
directly
• Slight __________________ in performance
– Avoid set/get method call overhead
154
Using protected Instance Variables
Disadvantages
• No ________________ checking
– subclass can assign illegal value
• Implementation dependent
– subclass methods more likely __________ on
superclass implementation
– superclass implementation changes may result in
subclass ___________________
• Fragile (brittle) software
155
Reexamine Hierarchy
• Use the best software engineering practice
– Declare instance variables as private
– Provide public _____________________ methods
– Use _____________ method to obtain values of
instance variables
• View new version of CommissionEmployee,
Figure 9.12
• New version of
BasePlusCommissiionEmployee, Figure 9.13
• Test program, Figure 9.14
156
Instantiating Subclass Object
Chain Of Constructor Calls
• Subclass constructor invokes superclass constructor
– __________ or _________________
• Base of inheritance hierarchy
– Last constructor called in chain is _________________
constructor
– _______________ subclass constructor’s body finishes
executing last
157
Instantiating Subclass Object
Chain Of Constructor Calls
• Example, Figure 9.15 : CommissionEmployee3BasePlusCommissionEmployee4 hierarchy
– CommissionEmployee3 constructor called second last
(last is Object constructor)
– CommissionEmployee3 constructor’s body finishes
execution second (first is Object constructor’s body)
• Figure 9.16, BasePlusCommissionEmploye5
• Figure 9.17, Test program, demonstrates
constructor calls
158
Software Engineering with
Inheritance
• At the design stage, certain classes found to be
closely related
– _______________ common attributes, behaviors
– Place these in a ____________________
– Use inheritance to develop subclasses with
inherited capabilities
• This avoids _____________ of classes,
"reinventing the wheel"
• Note
– Declaring a subclass ______________________
superclass source code
159
Object-Oriented Programming:
Polymorphism
Chapter 10
160
Problem with Subclasses
• Given the class hierarchy below
• Consider the existence of a draw function for each
subclass
• Consider also an _____________________ to the
superclass (which can also point to various objects
of the subclasses)
• How do you specify which __________ statement
to be called when using the references
Shape class hierarchy
Shape
Circle
Triangle
Right Triangle
Isosceles Triangle
Rectangle
Square
161
Introduction
• Polymorphism
– Enables “programming in the ______________”
– The same invocation can produce
“____________________” of results
• Interfaces
– Implemented by classes to assign common
functionality to possibly unrelated classes
162
Polymorphism
• When a program invokes a method through a
superclass variable,
– the correct ______________ version of the method
is called,
– based on the __________________ stored in the
superclass variable
• The same method name and signature can
cause different actions to occur,
– depending on the ________________ on which the
method is invoked
163
Polymorphism
• Polymorphism enables programmers to deal in
generalities and
– let the ______________ environment handle the
specifics.
• Programmers can command objects to behave
in manners appropriate to those objects,
– ___________________ the types of the objects
– (as long as the objects belong to the same
inheritance hierarchy).
164
Polymorphism Promotes
Extensibility
• Software that invokes polymorphic behavior
– independent of the ________________ to which
messages are sent.
• New object types that can respond to existing
method calls can be
– incorporated into a system without requiring
modification of the ____________________.
– Only client code that ______________ new objects
must be modified to accommodate new types.
165
Demonstrating Polymorphic
Behavior
• A superclass reference can be aimed at a
______________ object
– a subclass object “is-a” superclass object
– the type of the actual referenced _____________,
not the type of the _____________, determines
which method is called
• A subclass reference can be aimed at a
superclass object only if the object is
_________________
• View example, Figure 10.1
166
Polymorphism
• Promotes _____________________
• New objects types can respond to
______________ method calls
– Can be incorporated into a system without
modifying base system
• Only client code that instantiates the new
objects must be modified
– To accommodate ________________
167
Abstract Classes and Methods
• Abstract classes
– Are superclasses (called abstract superclasses)
– Cannot be _______________________
– Incomplete
• subclasses fill in "missing pieces"
• _______________________ classes
– Can be instantiated
– ________________ every method they declare
– Provide specifics
168
Abstract Classes and Methods
• Purpose of an abstract class
– Declare common ________________ …
– Declare common behaviors of classes in a class
hierarchy
• Contains one or more abstract _____________
– Subclasses must ______________
• Instance variables, concrete methods of
abstract class
– subject to normal rules of ______________
169
Abstract Classes
• Classes that are too ____________ to create
real objects
• Used only as abstract superclasses for
concrete subclasses and to declare
___________________
• Many inheritance hierarchies have abstract
superclasses occupying the top few levels
170
Keyword abstract
• Use to declare a class abstract
• Also use to declare a _____________
abstract
• Abstract classes normally contain one or
more abstract _______________
• All _____________ subclasses must
override all inherited abstract methods
171
Abstract Classes and Methods
•Iterator class
– __________________ all the objects in a
collection, such as an array
– Often used in polymorphic programming to
traverse a collection that contains references to
objects from various levels of a hierarchy
172
Abstract Classes
• Declares common attributes and behaviors of
the various classes in a class hierarchy.
• Typically contains one or more abstract
_______________
– __________________ must override if the
subclasses are to be concrete.
• Instance variables and concrete methods of an
abstract class subject to the normal rules of
inheritance.
173
Beware! Compile Time Errors
• Attempting to ______________ an object of an
abstract class
• Failure to ______________ a superclass’s
abstract methods in a subclass
– unless the subclass is also declared abstract.
174
Creating Abstract Superclass
Employee
•abstract superclass Employee,
Figure 10.4
– earnings is declared abstract
• ______________________ can be given for earnings
in the Employee abstract class
– An array of Employee variables will store
_____________ to subclass objects
• earnings method calls from these variables will call the
appropriate version of the earnings method
175
Example Based on Employee
Abstract Class
Concrete
Classes
176
Polymorphic interface for the
Employee hierarchy classes.
177
Note in Example Hierarchy
• Dynamic binding
– Also known as _____________ binding
– Calls to overridden methods are resolved at
______________ time, based on the type of object
referenced
• instanceof operator
– Determines whether an _____________ is an
instance of a certain type
178
How Do They Do That?
• How does it work?
– Access a derived object via __________________
– Invoke an abstract method
– At run time the __________________ of the
method is used
• Design of the V-Table
– Note description from C++
179
Note in Example Hierarchy
• Downcasting
– Convert a reference to a superclass to a
reference to a subclass
– Allowed only if the object has
an_____________relationship with the subclass
• getClass method
– Inherited from __________________
– Returns an object of type Class
• _______________ method of class Class
– Returns the class’s name
180
Superclass And Subclass
Assignment Rules
• Assigning a superclass reference to superclass
variable straightforward
• Subclass reference to subclass variable
straightforward
• Subclass reference to superclass variable ________
– because of is-a relationship
– Referring to subclass-only members through superclass
variables a compilation error
• Superclass reference to a subclass variable a
___________________
– Downcasting can get around this error
181
final Methods and Classes
•final methods
– Cannot be ______________ in a subclass
– ___________ and __________ methods implicitly
final
– final methods are resolved at __________ time,
this is known as static binding
• Compilers can optimize by inlining the code
•final classes
– Cannot be _____________ by a subclass
– All methods in a final class implicitly final
182
Why Use Interfaces
• Java has single _____________, only
• This means that a child class inherits from only
one parent class
• Sometimes multiple inheritance would be
convenient
• Interfaces give Java some of the advantages of
multiple inheritance without incurring the
disadvantages
183
What is an Interface?
• An interface is a collection of _____________
and method declarations
• The method declarations do not include an
_________________ (there is no method body)
184
What is an Interface?
• A child class that extends a parent class can
also _____________ an interface to gain some
additional behavior
• Implementing an interface is a
“______________” to include the specified
method(s)
• A method in an interface cannot be made
________________
185
When A Class Definition
Implements An Interface:
• It _____________________ each method in
the interface
• Each method must be public (even though the
interface might not say so)
• ________________ from the interface can be
used as if they had been defined in the class
(They should not be re-defined in the class)
186
Declaring Constants with Interfaces
• ________________ can be used to declare
constants used in many class declarations
– These constants are implicitly public, static
and final
– Using a __________________ declaration allows
clients to use these constants with just their names
187
Implementation vs. Interface
Inheritance
Implementation
Inheritance
• Functionality ______ in
the hierarchy
• Each new subclass
inherits one or more
methods declared in
superclass
• _____________ uses
superclass declarations
Interface Inheritance
• Functionality lower in
hierarchy
• Superclass specifies one
or more _________
methods
• Must be declared for
each class in hierarchy
• Overridden for subclass188
specific implementations
Creating and Using Interfaces
• Declaration begins with ________________
keyword
• Classes implement an _____________ (and
its methods)
• Contains __________________ methods
– Classes (that implement the interface) must
implement these methods
189
Creating and Using Interfaces
• Consider the possibility of having a class which
manipulates mathematical functions
• You want to send a function as a parameter
– Note that C++ allows this directly
– Java does not
• This task can be accomplished with interfaces
190
Creating and Using Interfaces
• Declare interface Function
• Declare class MyFunction which implements
Function
• Note other functions which are subclass objects
of MyFunction
• View test program which passes Function
subclass objects to function manipulation
methods
191
Graphical User Interface
Components: Part 1
Chapter 11
192
Graphical User Interface (GUI)
• Gives program distinctive “______________”
• Provides users with basic level of familiarity
• Built from GUI ________________ (controls,
widgets, etc.)
– User interacts with GUI component via mouse,
keyboard, etc
• Check out this visual index of components
193
Netscape Window With GUI
Components
button
menus
menu bar
combo box
scroll bars
194
Dialog Boxes
• Used by applications to interact with the user
• Provided by Java’s JOptionPane class
– Contains input dialogs and message dialogs
• View example program, Figure 11.2
195
Dialog Boxes
• Note icon
• Other icons available
Message dialog type
Icon
Description
ERROR_MESSAGE
A dialog that indicates an error to the user.
INFORMATION_MESSAGE
A dialog with an informational message to the
user.
WARNING_MESSAGE
A dialog warning the user of a potential
problem.
QUESTION_MESSAGE
PLAIN_MESSAGE
A dialog that poses a question to the user. This
dialog normally requires a response, such as
clicking a Yes or a No button.
no icon A dialog that contains a message, but no icon.
196
Some Basic GUI Components
Component
Description
JLabel
Displays uneditable text or icons.
JTextField
Enables user to enter data from the keyboard. Can also be used to
display editable or uneditable text.
JButton
Triggers an event when clicked with the mouse.
JCheckBox
Specifies an option that can be selected or not selected.
JComboBox
Provides a drop-down list of items from which the user can make a
selection by clicking an item or possibly by typing into the box.
JList
Provides a list of items from which the user can make a selection by
clicking on any item in the list. Multiple elements can be selected.
JPanel
Provides an area in which components can be placed and organized.
Can also be used as a drawing area for graphics.
197
Overview
• Swing GUI components
– Declared in package __________________
– Most are ____________ Java components
– Part of the Java Foundation Classes (JFC)
• Abstract Window Toolkit (AWT)
– ___________________ to Swing
– Declared in package java.awt
– Does not provide consistent, cross-platform lookand-feel
198
Lightweight
vs. Heavyweight
• Lightweight components
– Not tied directly to ________________________
supported by underlying platform
• Heavyweight components
– Tied directly to the ____________ platform
– AWT components
– Some Swing components
199
Superclasses of Swing’s
Lightweight GUI Components
• Class Component
– (package java.awt)
– ______________________ of Object
– Declares many behaviors and attributes common to
GUI components
200
Superclasses of Swing’s
Lightweight GUI Components
• Class Container
– (package java.awt)
– Subclass of Component
– _____________________ Components
201
Superclasses of Swing’s
Lightweight GUI Components
• Class JComponent
– (package javax.swing)
– Subclass of Container
– _________________ of all lightweight Swing
components
202
Common Lightweight Component
Features
• Pluggable look-and-feel
– _______________ the appearance of components
• Shortcut keys
– mnemonics
• Common ____________________ capabilities
• Brief description of component’s purpose
– tool tips
• Support for _____________________
203
Displaying Text and Images in a
Window
• Class JFrame
– Most windows are an instance or subclass of this
class
– Provides _______________________
– Provides min, max, close ______________
• Label
– ______________________ or information stating
the purpose of each component
– Created with class JLabel
204
Three Parts of a GUI Application
1. ________________________ that make up
the Graphical User Interface
2. ________________ that receive the events
and respond to them
3. ____________________ that does useful
work for the user
205
Events Generated by Swing
Components
Act that results in the event
Listener type
User clicks a button, presses Return
while typing in a text field, or chooses a
menu item
WindowListener
User closes a frame (main window)
User presses a
the cursor is over a component
User
component
while
over a
MouseListener
MouseMotionListener
Component becomes visible
ComponentListener
Component gets the keyboard focus
FocusListener
Table or list selection changes
ListSelectionListener
206
Events Generated by Swing
Components
• Each __________ is represented by an object
– Object gives information about the event
– Identifies the event _________________.
• Event sources are typically _____________,
– Other kinds of objects can also be event sources.
• Each event source can have _____________
listeners registered on it.
– Conversely, a
single listener can
register with
multiple event sources.
207
JLabel
• Label
– Provide ________________ on GUI
– Defined with class JLabel
– Can display:
• Single line of read-only text
• __________________________
• Text and image
• View Figure 11.6
– Note uses of the JLabel Class
208
Creating and Attaching label1
• Method setToolTipText of class
JComponent
– Specifies the tool tip
• Method add of class Container
– Adds a _________________ to a container
209
Creating and Attaching label2
• Interface Icon
– Can be added to a ________________ with
the setIcon method
– Implemented by class ImageIcon
210
Creating and Attaching label2
• Interface SwingConstants
– Declares a set of
___________________________________
such as those used to set the alignment of
components
– Can be used with methods
setHorizontalAlignment and
setVerticalAlignment
211
Creating and Attaching label3
• Other JLabel methods
– getText and ____________________
• For setting and retrieving the text of a label
– getIcon and setIcon
• For setting and retrieving the _______________
displayed in the label
– getHorizontalTextPosition and
setHorizontalTextPosition
• For setting and retrieving the horizontal position of the
text displayed in the label
212
Some basic GUI Components.
Constant
Description
Horizontal-position constants
SwingConstants.LEFT
SwingConstants.CENTER
SwingConstants.RIGHT
Place text on the left.
Place text in the center.
Place text on the right.
Vertical-position constants
SwingConstants.TOP
SwingConstants.CENTER
SwingConstants.BOTTOM
Place text at the top.
Place text in the center.
Place text at the bottom.
213
Other JFrame Methods
• setDefaultCloseOperation
– Dictates how the
____________________________ when the user
clicks the close button
• setSize
– Specifies the width and height of the __________
• setVisible
– Determines whether the window is displayed
(true) or not (false)
214
Event Handling
• An event occurs every time the user
– ________________ a character or
– Pushes a _________________________
• Any object can be ________________ of the
event.
• That object must:
– ________________ the appropriate interface
– Be registered as an event _____________ on the
appropriate event source.
215
Event Handling
• GUI's are _______________ driven
– Events occur when user interacts with GUI
– e.g., moving mouse, pressing button, typing in text
field, etc.
• Class java.awt.AWTEvent
• Checkout Sun tutorial on event handling
216
Some Event Classes Of Package
java.awt.event
217
Event Handling Model
• Three parts
– Event _________________
• GUI component with which user interacts
– Event _________________
• Encapsulates information about event that occurred
– Event _________________
• Receives event object when notified, then responds
• Programmer must perform two tasks
– ____________ event listener for event source
– Implement event-handling method (event handler) 218
Event Listener Object
• When a GUI program is running, each action of
the user generates an event
• The following are some types of events:
– Moving the ______________
– Clicking the mouse on a button
– ______________ some text into a text area
• For a program to respond to an event there
must be an ____________ object in the GUI
program that listens to that type of event
219
What is an Event Listener?
• An event listener is an _____________
– It "listens" for events from a specific GUI component
(itself an object)
• When an event is generated by the GUI
component
– A ____________ in the listener object is invoked to
respond to the event
220
What If …?
• When there is no event ______________ for an
event
– A program can ____________ events
– If there is no listener for an event, the event is just
ignored
221
Eventlistener
Interfaces
Of Package
java.awt.
event
222
Textfields
• JTextField
– __________ area in which user can enter text
• JPasswordField
– Extends JTextField
– ______________ characters that user enters
• View Figure 11.9
– Illustrates capabilities of textfields
– Note help on handling number fields
223
How Event Handling Works
• You must ______________ the event handler
– Through component’s method
addActionListener
224
How Event Handling Works
• The component knows to call
actionPerformed because …
– Event is _______________ only to listeners of
appropriate type
– Each event type has corresponding event-listener
interface
• Event _____________ specifies event type that occurred
225
Event Registration for
JTextField textField1
226
JButton
• Button
– Component user clicks to trigger a specific action
– Several different types
•
•
•
•
Command ________________
Check ________________
Toggle buttons
__________________ buttons
– javax.swing.AbstractButton subclasses
• Command buttons are created with class JButton
• Generate __________________________ when user
clicks button
227
Swing Button Hierarchy
228
JButton Example
• View, ButtonFrame class, Figure 11.15
• Test program, Figure 11.16
• Look for
– Declaration of the buttons
– Inner class ButtonHandler which does event
handling for the button
– Call to .addActionListener(handler) method
registers buttons to receive events
– The actionPerformed() method
229
Comments on JButton
• To detect when user clicks button
– Program must have an _______________ that
implements ActionListener interface
• Program must __________ object as an
action listener on the button (the event
source)
– Using the addActionListener method
230
Comments on JButton
• When user clicks the button, it fires an action
_________________.
– Results in the invocation of the action listener's
actionPerformed _____________
– The only method in the ActionListener
interface
• JButtons can have a __________ icon
– Appears when mouse is positioned over a button
– Added to a JButton with method
setRolloverIcon
231
Buttons That Maintain State
• Swing contains three types of ____________
buttons
•JToggleButton, JCheckBox and
JRadioButton
•JCheckBox and JRadioButton are
______________ of JToggleButton
232
JCheckBox
• Contains a check box ______________ that appears
to right of check box by default
• Generates an ItemEvent when it is ____________
– ItemEvents are handled by an ItemListener
– Passed to method _______________________
• Method isSelected returns whether check box is
selected (true) or not (false)
• View example class Figure 11.17
test Figure 11.18
233
JRadioButton
• Has two states – selected and unselected
• Normally appear in a _____________ in which
only one radio button can be selected at once
– Group maintained by a ButtonGroup object
• Declares method add to add a JRadioButton to
group
• Usually represents mutually ____________
options
• View RadioButtonFrame, Figure 11.19
Test program, Figure 11.20
234
Demonstration of JRadioButton
• When viewing Figure 11.19, look for the
following
– Declaration of JRadioButton references
– Group specification
– Instantiation of JRadioButton objects
– Registration of JRadioButton's to receive events
– RadioButtonHandler invokes method
itemStateChanged
235
JComboBox
• JComboBox
– List of items from which user can select
– Also called a drop-down list
• Note features in Figure 11.21
• Instantiate JComboBox to show three Strings
from names array at a time
• Register JComboBox to receive events
• ItemListener invokes method
itemStateChanged
236
JList
• A list is a series of items
– User can _____________ one or more items
– Single-selection vs. multiple-selection
• JList demonstration, Figure 11.23
– Note use of ColorNames array to populate JList
– Specification of SINGLE_SELECTION
– Registration of JList to __________ events
– ListSelectionListener invokes method
valueChanged
– Background set according to user choice
237
Multiple-Selection Lists
• Multiple-selection list capabilities
– Select ______________ items from Jlist
– Allows continuous _________ selection
• Look for the following in Figure 11.25
• Use of ColorNames array
– Specification of MULTIPLE_INTERVAL_SELECTION
option
– Use of JButton and JListCopyList method
238
Mouse Events
• Create a MouseEvent object
• Handled by MouseListeners and
MouseMotionListeners
• MouseInputListener combines the two
interfaces
• Interface MouseWheelListener declares
method mouseWheelMoved to handle
MouseWheelEvents
239
Mouse Event Handling
• Event-listener interfaces for mouse events
– MouseListener
– MouseMotionListener
– Listen for MouseEvents
• In Figure 11.28 note use of…
– Register JFrame to receive mouse events
– Methods invoked for various mouse events
• (Note that program does not seem to perform as
advertised when run under ReadyTo !!?)
240
Listener Interfaces
MouseListener and MouseMotionListener interface methods
Methods of interface MouseListener
public void mousePressed( MouseEvent event )
Called when a mouse button is pressed while the mouse cursor is on a
component.
public void mouseClicked( MouseEvent event )
Called when a mouse button is pressed and released while the mouse
cursor remains stationary on a component. This event is always
preceded by a call to mousePressed.
public void mouseReleased( MouseEvent event )
Called when a mouse button is released after being pressed. This
event is always preceded by a call to mousePressed and one or
more calls to mouseDragged.
public void mouseEntered( MouseEvent event )
Called when the mouse cursor enters the bounds of a component.
241
Listener Interfaces
MouseListener and MouseMotionListener interface methods
public void mouseExited( MouseEvent event )
Called when the mouse cursor leaves the bounds of a component.
Methods of interface MouseMotionListener
public void mouseDragged( MouseEvent event )
Called when the mouse button is pressed while the mouse cursor is on
a component and the mouse is moved while the mouse button remains
pressed. This event is always preceded by a call to mousePressed.
All drag events are sent to the component on which the user began to
drag the mouse.
public void mouseMoved( MouseEvent event )
Called when the mouse is moved when the mouse cursor is on a
component. All move events are sent to the component over which the
mouse is currently positioned.
242
Listener Interfaces
• Suppose your class directly implements
MouseListener,
– Then you ___________________ all five
MouseListener methods.
– Even if you care only about mouse clicks
• Methods for those events you don't care about
can have ______________ bodies.
– Resulting collection of empty method bodies can
make code harder to read and maintain
243
Adapter Classes
• Solution is to use __________________
classes
• For example, the MouseAdapter class
implements the MouseListener interface.
• An adapter class implements ____________ of
all its interface's methods.
244
Adapter Classes
• To use an adapter
– Create a ________________ of it, instead of
directly implementing a listener interface.
– By extending MouseAdapter, your class
_________________ empty definitions of all five of
the methods that MouseListener contains.
245
Adapter Classes
• Characteristics of an adapter class
– _________________ interface
– Provides ________________ implementation of
each interface method
– Used when all methods in interface is not needed
Event-adapter class in java.awt.event
Implements interface
ComponentAdapter
ContainerAdapter
FocusAdapter
KeyAdapter
MouseAdapter
MouseMotionAdapter
WindowAdapter
ComponentListener
ContainerListener
FocusListener
KeyListener
MouseListener
MouseMotionListener
WindowListener
246
Adapter Classes
• Example of use of an adapter class
– Figure 11.34 , the Painter program
• Note
– Registration of MouseMotionListener to listen
for window’s __________________ events
– ____________________ method mouseDragged,
but not method mouseMoved
– Store ________________ where mouse was
dragged, then repaint JFrame
247
Extending MouseAdapter
• The MouseDetails.java program,
Note example, Figure 11.31
• Demonstrates
– How to determine the __________ of mouse clicks
– How to distinguish between _______________
mouse buttons
248
InputEvent Methods
• Help distinguish among
– left-,
– center- and
– right-mouse-button clicks
InputEvent method Description
isMetaDown()
Returns true when the user clicks the right mouse button on a
mouse with two or three buttons. To simulate a right-mousebutton click on a one-button mouse, the user can hold down the
Meta key on the keyboard and click the mouse button.
isAltDown()
Returns true when the user clicks the middle mouse button on
a mouse with three buttons. To simulate a middle-mousebutton click on a one- or two-button mouse, the user can press
the Alt key on the keyboard and click the only- or left-mouse
button, respectively.
249
Key Event Handling
• Interface KeyListener
• Handles key events
– Generated when keys on keyboard are pressed and
released
• KeyEvent
– Contains ___________________ that represents
key
• Demonstrated in Figure 11.36
250
Layout Managers
• Layout manager capabilities
– Provided for _________________ GUI components
– Provide basic layout capabilities
– Processes layout details
– Programmer can concentrate on basic “look and
feel”
– Interface LayoutManager
251
Layout Managers
• Layout manager methods
Layout manager Description
FlowLayout
Default for javax.swing.JPanel. Places components sequentially
(left to right) in the order they were added. It is also possible to
specify the order of the components by using the Container method
add, which takes a Component and an integer index position as
arguments.
BorderLayout
Default for JFrames (and other windows). Arranges the components
into five areas: NORTH, SOUTH, EAST, WEST and CENTER.
GridLayout
Arranges the components into rows and columns.
252
FlowLayout
• _____________________ layout manager
• GUI components placed in container from
_________ to ______________
• Example program, Figure 11.39
– Layout set as FlowLayout
– Note results as user presses button
253
BorderLayout
• Arranges components into five ___________
– NORTH
– SOUTH
– EAST
– WEST
– CENTER
(top of container)
(bottom of container)
(left of container)
(right of container)
(center of container)
• View example, Figure 11.41
254
GridLayout
• Divides container into grid of specified
___________________________
• Components are added starting at top-left cell
– Proceed left-to-fight until ____________ is full
• GridLayout demonstration, Figure 11.43
– Clicking buttons toggles between different layouts
255
Panels
• Helps organize components
• Class JPanel is ____________ subclass
• May have components (and other
_____________) added to them
• Panel example, Figure 11.45
256
Applying Concepts
• Suppose you wish to have a GUI which
accomplishes the following
– Enter numbers
in text boxes
– Press button
to do
calculations
257
Step By Step
• View code to create the window
• Note
– Class (program) extends JFrame
– Constructor sets up window using methods
inherited from JFrame
– Method main()instantiates class object
258
Add the Text Labels
• View additional code
• Note
– Declaration, instantiation of JLabels
– Container reference, pane
Gets handle for contentPane
– pane layout specified
– JLabels added
259
Add the Text Boxes
• View next iteration of code for adding the
JTextFields
• Note
– Declaration, instantiation of JTextFields
– Change grid layout of pane for 2 columns
– Adding to pane
260
Final Version
• View final code version
• Note
– Declaration, instantiation of buttons
– Declaration, definition, instantiation of action
handlers
• Different author, does not use inner anonymous classes
– Add action handlers to the buttons
• Our program never actually calls the action
handlers
261
Implement an Event Handler
Every event handler requires three bits of code:
1. Code that specifies that the class either
1. Implements a listener interface or
2. Extends a class that implements a listener interface.
For example:
public class MyClass implements ActionListener {…
2. Code that registers an instance of the event
handler class as a listener upon one or more
components.
For example:
someComponent.addActionListener(instanceOfMyClass);
3. Code that implements the methods in the listener
interface.
For example:
public void actionPerformed(ActionEvent e)
{ ...//code that reacts to the action... }
262
Exception Handling
Chapter 13
263
Motivation
• We seek
programs
• When something unexpected occurs
– Ensure program ________________________ the problem
– Then program must do something about it
• Extensive testing of special situations can result in
"____________________ code"
• Need mechanism to check for problem where it could
occur
• When condition does occur
– Have _________________ to code to handle the problem
264
Overview
• Exception
– Indication of ___________________ during execution
• Uses of exception handling
– Process exceptions from program components
– Handle exceptions in a uniform manner ______________
– Remove ___________ code from “main line” of execution
• A method detects an error and throws an exception
– Exception handler processes the error
– Uncaught exceptions yield _____________ effects
• Might terminate program execution
265
Overview
• Code that could generate errors put in
________ blocks
– Code for error handling enclosed in a __________
clause
– The ____________ clause always executes
• Termination model of exception handling
– The block in which the exception occurs expires
• throws clause specifies _____________
method throws
266
Exception Handler
Exception
"thrown" here
Thrown exception matched against
first set of exception handlers
Exception
handler
If it fails to match, it is matched against
set of handlers, etc.
Exception
handler
If exception matches ___________ of
handlers, program is abandoned
267
Example
• Consider the problem of division by zero
• Note elements of Figure 13.1
– try block
– Following catch blocks
– throws specification
268
Sequence of Events for throw
Preceding step
try block
throw
statement
unmatched catch
matching catch
unmatched catch
next step
269
Sequence of Events for
No throw
Preceding step
try block
throw
statement
unmatched catch
matching catch
unmatched catch
next step
270
Java Exception Hierarchy
• __________________ Throwable
– Subclass ________________
• Exceptional situations
• Should be caught by program
– Subclass ______________
• Typically not caught by program
• Checked exceptions
– Catch or _________________
• Unchecked exceptions
271
Inheritance hierarchy for class
Throwable
Throwable
Exception
RuntimeException
IOException
Error
AWTError
ThreadDeath
OutOfMemoryError
272
Handling Exceptions
• Rethrow exception if catch
cannot handle it
• Resource leak
– Caused when _____________________________
by a program
• The finally block
– Appears after catch blocks
– Always ________________
– Optional
– Use to release resources
273
Using finally
• View program, Figure 13.3
• Note
– __________________ of exception
– Code for throw exception
– Blocks using ________________
• Suggestion
– Do not use a try block for ____________________
which may cause a problem
– Enclose _____________________ of statements
– Follow by _______________ catch blocks
274
Sequence of Events for
finally clause
Preceding step
try block
throw
statement
unmatched catch
matching catch
unmatched catch
finally
next step
275
Stack Unwinding
• Exception not caught in scope
– Method _________________
– Stack ______________________ occurs
– Another attempt to catch exception
• View Figure 13.4
• Note
– Sequence of events during run
– Resulting output
276
printStackTrace, getStackTrace
and getMessage
• Throwable class
– Method printStackTrace
• Prints method call __________________
– Method getStackTrace
• Obtains stack-trace information
– Method getMessage
• Returns _____________________ string
• View example of these, Figure 13.5
277
Chained Exceptions
• Useful for a catch handler to
– Catch one exception type
– Then throw a new exception of ________________
– Indicates program-specific exception
• Chained exceptions enable
– Exception object to ____________________ info
• Figure 13.6 demonstrates use of chained
exceptions
278
Multithreading
Chapter 23
279
Introduction
• Consider ability of human body to ___________
– Breathing, heartbeat, chew gum, walk …
• In many situations we need a computer to
multitask
• Concurrency normally available in __________
• Java provides built-in multithreading
– Multithreading improves the ___________ of some
programs
280
Thread States: Life Cycle of a
Thread
• __________________ state
– New thread begins its life cycle in the new state
– Remains in this state until program starts the
thread, placing it in the runnable state
• runnable state
– A thread in this state is ___________ its task
• waiting state
– A thread ___________ to this state to wait for
another thread to perform a task
281
Thread States: Life Cycle of a
Thread
• __________________ state
– A thread enters this state to wait for another
thread or for an amount of time to elapse
– A thread in this state returns to the ___________
state when it is signaled by another thread or
when the timed interval expires
• terminated state
– A runnable thread enters this state when it
_____________ its task
282
Operating System View Of
runnable State
• ready state
– ____________ waiting for another thread
– Waiting for the ______________ to assign the
thread a processor
283
Operating System View Of
runnable State
• running state
– Currently has a _________________ and is
executing
– Often executes for a small amount of processor
time called a _______________________ before
transitioning back to the ready state
284
Thread Priorities and Thread
Scheduling
• Java thread priority
– Priority in range ______________
• Timeslicing
– Each thread assigned time on the processor (called
a quantum)
– Keeps ______________ threads running
285
Thread.MAX_PRIORITY
Priorities
and
Scheduling
286
Creating and Executing Threads
•Runnable interface
– Preferred means of creating a multithreaded
application
– Declares method _______________
– Executed by an object that implements the
Executor interface
•Executor interface
– Declares method ___________________
– Creates and manages a group of threads called
a thread pool
287
Creating and Executing Threads
•ExecutorService interface
– ______________________ of Executor that
declares other methods for managing the life cycle
of an Executor
– Can be created using _______________ methods
of class Executors
– Method shutdown _______________ when tasks
are completed
288
Creating and Executing Threads
•Executors class
– Method newFixedThreadPool creates a pool
consisting of a __________________________ of
threads
– Method newCachedThreadPool creates a pool
that creates new threads
_____________________________
289
Creating and Executing Threads
• PrintTask class Figure 23.4
• RunnableTester, Figure 23.5
• Demonstrates
– ____________ Thread objects
– Using Thread methods ___________ and sleep
– Creates 3 equal priority threads
– Each is put to sleep for random number of
milliseconds
– When awakened, it displays name, etc.
290
Producers and Consumers
• Producer
– Generating
_______________
• Consumer
– Receives and
_________________
the output
291
Synchronization
• Problem
– Sometimes the producer gets too far
____________ of the consumer
• The objects produced fill up the holding area
(_____________)
• The producer must wait for space to place objects
– Sometimes the ______________ gets ahead of the
producer
• There are no objects to be processed (_____________
buffer)
• The consumer must wait for the producer
292
Thread Synchronization
• Thread synchronization
– Provided to the programmer with
_____________________
• Exclusive access to a shared object
– Implemented in Java using _____________
•Lock interface
– lock method obtains the lock, enforcing mutual
exclusion
– unlock method ________________ the lock
– Class ReentrantLock implements the Lock
293
interface
Thread Synchronization
• Condition variables
– If a thread holding the lock cannot continue with its
task until a condition is satisfied, the thread can wait
on a ____________________
– Create by calling Lock method newCondition
– Represented by an object that implements the
___________________ interface
294
Thread Synchronization
• Condition interface
– Declares methods await, to make a thread wait,
– ____________________, to wake up a waiting
thread, and
– signalAll, to wake up all waiting threads
295
Producer/Consumer Relationship
without Synchronization
• Buffer
– ____________________ memory region
• Producer thread
– Generates _____________ to add to buffer
– Calls wait if consumer has not read previous message in
buffer
– Writes to empty buffer and calls ____________ for
consumer
• Consumer thread
– Reads data from buffer
– Calls wait if buffer ________________
• Synchronize threads to avoid corrupted data
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Producer/Consumer Relationship without
Synchronization
• View source code which establishes
– Buffer, Figure 23.6
• An interface which specifies get and set methods
– Producer, Figure 23.7
•
•
•
•
___________________ of Thread
Uses a shared Buffer object
Method run is _________________ from Thread class
Uses Buffer.set() method
– Consumer, Figure 23.8
• Also a subclass of Thread, also uses shared Buffer
• Uses the Buffer.get() method
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Producer/Consumer Relationship without
Synchronization
• View Figure 23.9 which implements the
Buffer interface
– Implements the _________________ methods
• This UnsynchronizedBuffer object is used
in Figure 23.10 program
– Buffer object declared, instantiated
– Also Producer and Consumer objects
– Both threads call method start()
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Producer/Consumer Relationship without
Synchronization
• Example randomly called producer and
consumer
• You should note that in some cases the data
was _________________
– Consumer reads values _________ producer
generates
– Consumer _______________ a value
– Consumer reads same value multiple times
• We need to deal with problem so data is not
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corrupted
Producer/Consumer Relationship with
Synchronization
• Solution is to _________________ the
producer and consumer objects
• Figure 23.11 implements a buffer and
synchronizes
– Consumer consumes only ______ produces a
value
– Producer produces a value only after consumer
consumes ____________ value produced
– Condition variable occupiedBufferCount
determines whose turn it is
• Program which uses this, Figure 23.12
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Using Thread Methods
• Create Wait class
• Has _______________ methods
• Provide capability to have another application
______________ for a certain amount of time
• Note Example to act as a simple timer.
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Circular Buffer
• Features
– Multiple memory cells
– Produce item if one or more empty cells
– Consume item if one or more filled cells
• Caveats
– Producer and consumers must be relatively
______________ speed
• Otherwise buffer fills up or stays empty
– Synchronization still necessary
– Seek to optimize buffer size
• ______________________ thread-wait time
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Circular Buffer
• Circular Buffer class Figure 23.13
– ______________ for mutual exclusion
– Condition variables to control writing and reading
– Circular buffer; provides three spaces for data
– Obtain the lock ____________ writing data to the
circular buffer
– Wait until a buffer space is ___________
– Impose circularity of the buffer
– ___________ waiting thread when to read data
from buffer
– Release lock
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Circular Buffer
• Circular Buffer test, Figure 23.14
– Create instance of circular buffer
– Execute producer, consumer in separate threads
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Daemon Threads
• Run for benefit of _____________________
– Do not prevent program from terminating
– __________________ is a daemon thread
• Set daemon thread with method setDaemon
– Must be done at __________________ time
• Do not assign _____________ tasks to daemon
thread
– Will be terminated without warning
– May prevent those tasks from completing properly
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Runnable Interface
• May be necessary to __________ a class that
already extends a class other than Thread
• Java does not allow a class to extend more
than one class at a time
– Implement Runnable for ____________ support
• Program that uses a Runnable object to
control a thread
– Creates a Thread object
– Associates the Runnable object with that Thread
class
306
Runnable Interface
• Illustration of using a Runnable interface
– Figure 23.18
• Note methods start, stop, run
307
Files and Streams
Chapter 14
308
Introduction
• Storage of data in variables is ___________
– when the program is done running,
when computer is turned off
The data is gone!
• Data stored permanently (more or less) on
secondary storage devices
– magnetic ____________
– ___________ disks
– tapes
• We consider creation & use of files of data
309
The Data Hierarchy
• Lowest level of data storage is in
____________________
– 0s and 1s -- bits
• Bits grouped together into _______________
• Bytes grouped into characters
• Characters and/or bytes grouped together to form
_________________
• Fields grouped together to form records
• Records grouped to form files
310
The Data Hierarchy
311
Sequential Devices -- Some History
• Tape Drives
312
Data Stored on Tape
Interblock Gap for
purpose of
_______________
or deceleration of
tape past the
read/write head.
Result is large
percentage of tape
length ___________
on the gaps.
313
Data Stored on Tape
Records
_______________
in groups to save
space wasted by
the required gaps
314
Disk Components
• Cylinders
• Tracks
• Sectors
315
Disk Components
• _______________
heads move in and out
• Possible to have multiple
fixed heads
• Need head for each
_____________ surface
• __________________
of data on inside as
outside tracks
316
Disk Components
• Track
• Sector
• Inner sectors have
same amount of data
as outer outer (why?)
• Outer sectors less
____________ (bits
per inch)
317
Timing Components
• Access motion time (_____________ time)
– motion of read/write heads between tracks
– this is the most
time of the three
• Rotational delay
• Data __________ time
318
Storage of Sequential Files
• Any type of serial access storage device
– originally ___________________
– magnetic tape
– even punched paper tape!
• Now would be placed on __________________
devices (disks)
319
Files and Streams
• Java views a file as a stream of __________
• File ends with end-of-file marker or a specific byte
number
• File as a stream of bytes associated with an object
– Java also associates streams with _____________
•System.in, System.out, and System.err
• Streams can be redirected
320
Files and Streams
• File processing with classes in package
java.io
– FileInputStream for
____________________ input from a file
– FileOutputStream for
byte-based ________________ to a file
– FileReader for
-based
input from a file
– ________________ for character-based
output to a file
321
Files and Streams
• Buffering
– ____________________ performance of I/O
– Copies each output to a region of memory called a buffer
• We can send the entire buffer to disk ___________
– One long disk access takes ____________________ than
many smaller ones
– Due to repeated head seeks required
• BufferedOutputStream buffers file output
• BufferedInputStream buffers file input
322
Class File
• Methods from class File
Method
boolean canRead()
Description
Returns true if a file is readable; false otherwise.
boolean canWrite()
boolean exists()
Returns true if a file is writable; false otherwise.
Returns true if the name specified as the argument to the File constructor is a file or directory
in the specified path; false otherwise.
boolean isFile()
Returns true if the name specified as the argument to the File constructor is a file; false
otherwise.
Returns true if the name specified as the argument to the File constructor is a directory;
false otherwise.
Returns true if the arguments specified to the File constructor indicate an absolute path to a
file or directory; false otherwise.
boolean isDirectory()
boolean isAbsolute()
String
getAbsolutePath()
Returns a string with the absolute path of the file or directory.
String getName()
String getPath()
String getParent()
Returns a string with the name of the file or directory.
Returns a string with the path of the file or directory.
Returns a string with the parent directory of the file or directory—that is, the directory in which
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the file or directory can be found.
Class File
• Methods from class File
Method
String getName()
Description
Returns a string with the name of the file or directory.
String getPath()
String getParent()
Returns a string with the path of the file or directory.
Returns a string with the parent directory of the file or directory—that is, the directory in which
the file or directory can be found.
long length()
Returns the length of the file, in bytes. If the File object represents a directory, 0 is returned.
long lastModified()
Returns a platform-dependent representation of the time at which the file or directory was last
modified. The value returned is useful only for comparison with other values returned by this
method.
Returns an array of strings representing the contents of a directory. Returns null if the File
object is not a directory.
String[] list()
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Class File
• View Figure 17.4
– Creates a GUI with JTextField
– Enter file, directory name
– _________________ displays information
• Program features
– Body of if outputs information about file if it exists
–
–
–
–
Test if object is ______________, test if file exists
Create a reader to gather data from file
Read text _________________ in file
Get list of files in directory
325
Creating a Sequential-Access File
• Java imposes __________________ on a file
• _______________________ structures file
according to application
• AccountRecord class specified in
Figure 17.6 declares structure for file access
examples … note …
– Class compiled into _______________
– Imlements ________________ for use without
I/O streams
326
Creating a Sequential-Access File
• Program in Figure 17.5 prepares GUI's for file
access program
• Note
– Class compiled as a package
– Buttons provided for actions in later examples
– Generic doTask buttons
327
Creating a Sequential-Access File
• Program in Figure 17.7 imports the GUI and
record classes
– Interface and references to buttons created
– Instantiate, assign JFileChooser object
– Selected file retrieved, opened
– Method closeFile to close current file
– Data retrieved from text fields
– New record retrieved, written to file
328
Reading Data from Sequential Access Files
• Data stored in files
• Retrieved for processing when needed
• Accessing a sequential file
– Data must be read in ________________ it was written
• Note program of Figure 17.9
–
–
–
–
Create instance of interface
Respond to Open button, Next button
JFileChooser used as before
Method _______________ reads an Object from the
ObjectInputStream
329
Reading Data from Sequential Access Files
• To read from file repeatedly
– Must close and reopen file
• Each time through
– Print only records which _________________
• Figure 17.19 allows inquiries
– Note ____________ of FileInputStream in
ObjectInputStream
– Note use of _______________ for
EOFException
330
Updating Sequential Access Files
• Difficult to ____________ a sequential-access
file
– Entire file must be rewritten to change one field
– Only acceptable if many records being updated at
once
• Note that this was done in the days of using
magnetic tapes
331
Characteristics of Sequential Systems
• Two types of files
– ___________ files -- files with relatively
permanent data
– Transaction files -- file of _____________ records
• Updating master files
– use transaction files
– combine (_____________) old master with
transaction file
– create new master file
– Old master and Transaction file are the
_____________ for the New Master
332
Updating Master Files
Old Master
File
Transaction
Update
Program
Exception
Report
New Master
333
Updating Master Files
• Transaction file contains
– _______________ to be added
– modifications to __________ records on old master
– orders for deletions of records on the old master
• Possible errors
– Adding => record for specified ID __________
exists
– Modify => record does not exist
– _____________ => record does not exist
334
Program Flow Chart
Open files, read 1st records
Trans Key < OM key
Compare
keys
Trans key > OM key
Trans key = = OM key
Type of
Trans
Add OK
Other,
Error
Type of
Trans
Del,
go on
Other,
Error
Write OM
record to
NM file,
Trans key
yet to be
matched
Modify, Make changes
335
Sequential Update
336
Sequential Update
Transaction File
Old Master
10
20
25
30
35
40
50
55
80
10
20
30
40
50
60
70
80
90
100
M
M
I
D
D
A
M
M
M
New Master
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Random-Access Files
• “Instant-access” applications
– Record must be located ______________
– Transaction-processing systems require rapid
access
• Random-access files
– Access individual records directly and quickly
– Use _______________ for every record
• Easy to calculate record locations
– Insert records without ______________ other data
338
in file
Java's View of Random-Access File
339
Creating a Random-Access File
• RandomAccessFile objects
– Like DataInputStream and
DataOutputstream
– Reads or writes data in spot specified by fileposition pointer
• Manipulates all data as ____________________
• Normally writes one ______________ at a time to file
• Note Figure 17.12, a new class derived from
AccountRecord
340
Creating a Random-Access File
• RandomAccessAccountRecord of Figure
17.12 adds features
– Two ________________________
– Routine to read a record
– Routine to _______________ a record
• These will be used in the application to create a
Random file, Figure 17.13
– Window to name and open the new file
– Program generates 100 empty records
341
Writing Data Random-Access File
• Figure 17.14
– Opens the file previously created
– First window has ______________ button, Open
dialog box appears
– Uses BankUI graphical interface
– Click _______________ button to save the record
• RandomAccessFile method ____________
– Determines location in file where record is stored
– Sets file-position pointer to a specific point in file
342
Reading from Random-Access File
• Read
file, Figure 17.15
through random-access
– Opens the RandomAccessFile, specify file name
with Open file dialog box
– Record displayed in BankUI window
– Click on _____________ button to view next record
– _________________ combination handles end of
file
343
Transaction-Processing
Program
• Substantial transaction-processing system,
Figure 17.21 class with methods for
– Uses random-access file
– Updates, adds and deletes accounts
• Note
– Creation of ________________ object
– Handling of action buttons
– Creating new records
– Updating, deleting records
– __________________ records in text fields
344
Transaction-Processing
Program
• FileEditor program, Figure 17.22
• Uses the TransactionProcessor class
• Features
– Create RandomAccessFile from name provided
– Position ______________________
– Read, edit,
– Reposition file pointer, update record
– Delete record by ____________________
345