Slide 1
Welcome to CMSC298P







CMSC298P – Coordinator: Nelson Padua-Perez
TA’s Office Hours (TBA)
Homework
 Check class web site1
 Install Eclipse
 Go over the Eclipse Tutorial (see web page entry)
 Write and compile all the programs discussed in lecture
Mac environment for labs
We will distribute accounts tomorrow
Going over the syllabus
Required
 Attendance
 Working on homework
1
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 2
Modern Program Development
Old way:
Text editor (vi, emacs): Program source is typed in and modified.
Compiler:
Debugger:
Modern way:
(IDE)
Examples:
2
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 3
The Java Programming Language
Java – Why is i t special?
– An object-oriented programming language
– Developed in early 1990’s.
– Unlike C++, Java programs are portable between machines – why?
• C/C++ programs …
• Java bytecode.
• A JVM interpreter ….
– Has a rich set of libraries.
– The Java compiler and interpreter are part of Java Software
Development Kit (SDK), also referred to as Java Development Kit
(JDK).
3
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 4
Java Programming Concepts
A quick overview of fundamental Java concepts. (More details
later.)
Object:
Class: blueprint .
Method:
Main Method:
Statements: Individual instructions. Examples:
Declarations –
Assignment –
Method invocation –
Control flow –
4
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 5
A Sample Java Program
/**
* My first sa mple Java program.
File: MyFirstP rogra m.java
*/
public cla ss MyFirstP rogra m {
public static void m ain( String[ ] arg s ) {
int secondsPerMinute = 60;
// let’ s crea te some varia ble s
int minutesPe rLectu re = 50;
int tota lSeconds = secondsP erMinute * minutesP erL ecture;
System.out.println( " The re a re " + to talSeconds + " seconds in a lec ture.“ );
}
}
Program Output:
There are 3000 sec onds in a lectur e.
5
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 6
A Sample Java Program
There are 3000 seconds in a lecture.
6
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 7
A Sample Java Program
There are 3000 seconds in a lecture.
7
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 8
A Sample Java Program
There are 3000 seconds in a lecture.
8
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 9
Java Program Organization
Class: The structure around which all Java programs are based.
File name: MyFirstProgram.java:
public class My FirstProgram {
… (contents of the class go here) …
}
A class consist of a combination of data units, called variables,
and computation units, called methods.
9
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 10
Java Program Organization
Methods: This is where all the computa tion begins.
public static void main( String[ ] a rgs ) {
… (contents of the main method go here ) …
}
Variables: These are the data i tems tha t the methods operate on.
Variables can be of various types, integers, for example:
int secondsPerMinute = 60;
int minutesPerLecture = 50;
10
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 11
Java Program Organization
Statements:
Declarations –
int x, y, z;
String s = “Howdy”;
boolean isValid = true;
// three integer va riable s
// a character string variable
// a boolean (true or false) variable
Assignments –
x = 13;
Method invocation –
System.out.p rintln( “Print this message“ );
Control flow –
Expressions/Operators:
x = (2*y – z)/32;
11
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 12
Other Java Elements: Comments
Comments: :
Line comments:
Block comments:
interest = ba lance * rate;
/* The following lines of code update
the ba lance and compute the account
interest. */
balance = oldBalance – debits;
interest = ba lance * rate;
// compute the account interest
/* The following lines of code update
* the ba lance and compute the account
* interest.
*/
balance = oldBalance – debits;
interest = ba lance * rate;
It is the block stand out better.
12
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 13
Java I/O and JOptionPane
Java Input/Output:
JOptionPane:
Input dialog:
showInputDialog( String prompt ):
String name;
name = JOptionPane.showInputDialog( "Enter your name“ );
name  “Schultzie von Wienerschnitzel III”
13
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 14
More JOptionPane
Message Dialog:
JOptionPane.showMessageDialog( null, “Your message here” );
Why the null? Don’t
worry, just include it.
14
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 15
Java Example with JOptionPane
File:J OPSa mple.java
/**
* A simple exa mple sho wing Java I/ O using JOp tionPane
*/
import java x. swing.*;
// needed to make JOp tionPane accessible
public cla ss J OPSample {
public static void m ain( String[ ] arg s ) {
String nam e = JOptionPane. sho wInputDialog( "Enter you r name“ );
String reply = "Nam e entere d is: " + nam e;
JOptionPane.showM essageDialog ( null, rep ly );
System. exit(0 );
// terminate the program
}
}
15
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 16
Dissecting the Example
/**
* A simple example showing Java I/O using JOptionPane
*/
import javax.swing.*;
// needed to make JOptionPane accessible
public class JOP Sample {
public static void main( String[ ] a rgs ) {
String name = JOptionPane.showInputDialog( "Enter your name“ );
String reply = "Nam e entered is: " + name;
JOptionPane.showMessageDialog( null, reply );
System. exit(0);
// terminate the program
}
}
16
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 17
Still More on JOptionPane
Confirmation Dialog:
int answer;
answer = JOptionPane.showConfirmDialog(
Java
Again,null,
alway s “Isn’t
include this.
great?" );
• JOptionPane. YES_OPTION
• JOptionPane. NO_OPTION
• JOptionPane. CANCEL_OPTION
if “Yes”
if “No”
if “Cancel”
17
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 18
Another Example with JOptionPane
import java x. swing.*;
File:J OPSa mple2.java
public cla ss J OPSample2 {
public static void m ain( String[ ] arg s ) {
String nam e = JOptionPane. sho wInputDialog( "Enter you r name" );
String cofirmMe ssage = "Is your nam e re ally " + name + "?";
int answe r = JOp tionPane.showConfirmDialog( null, cofirmMe ssage );
if (answe r == JOptionPane.YES_ OPTI ON ) {
JOptionPane.showM essageDialog ( null, "He llo " + name );
} else {
JOptionPane.showM essageDialog ( null, "You lied!" );
}
System. exit(0 );
// terminate (nee de d with JOp tionPane)
}
}
18
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 19
Eclipse Introduction
•
•
•
•
•
How to start Eclipse
How to create a Project
How to create a program
– “Hello World”
– JOPSample2
How to compile a program
How to run a program
19
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 20
Primitive Data Types
Java’s primitive data types:
Integer Types:
int
byte, short
long
Floating-Point Types:
float
double
Other types:
boolean
char
String (?): is not a primitive type.
20
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 21
Data Types and Variables
Strong Type Checking: Java checks that all expressions
involve compatible types.
int x, y;
double d;
String s;
boolean b;
char c;
Foolish
human
x
b
c
s
d
=
=
=
=
=
7;
true;
‘#’;
“cat” + “bert”;
x – 3;
b = 5;
y = x + b;
c = x;
21
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 22
Common Numeric Operators
Arithmetic Operators:
– Unary negation:
– Multiplication/Division
– Addition/Subtraction:
Comparison Operators:
– Equality/Inequality:
– Less than/Greater than:
– Less than or equal/Greater than or equal:
22
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 23
Common String Operators
String Concatenation: The ‘+’ operator concatenates (joins) two
strings.
String Comparison:
s.equals(t) :
s.compareTo(t) :
23
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 24
Converting (Parsing) Strings to Numbers
Parsing:
String  int:
int year = Integer.parseInt( “2004” )
String  float:
float weight = Float.parseFloat( “175.35” );
String  double:
double pi = Double.parseDouble( “3.1415926” ):
Example:
String heightStri ng = JO ptionPane .show InputDialog( “Enter height ” ) ;
float height = Float .parseFl oat( heightStri ng );
24
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 25
Control Flow and Conditionals
Control flow:
Conditionals:
– Loops:
The if statement:
if ( inchesOfSnow > 7 )
System.out.println( “I’m staying home” );
The if-else statement:
if ( inchesOfSnow > 7 )
System.out.println( “I’m staying home” );
else
System.out.println( “I’m staying home anyway” );
25
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 26
More on Conditionals
Basic Structure:
Logical Operators:
Logical “and”: &&
Logical “or”: ||
Logical “not”:
)
if ( temp >= 97 && temp <= 99 )
System.out.println( “Patient is healthy” );
if ( months >= 3 || miles >= 3000 )
System.out.println( “Change your oil” );
!
if ( ! phone.equals( “301-555-1212” )
System.out.println( “Sorry, wrong number” );
26
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 27
Example of Conditionals
/**
* An examp le using J OptionPane and con ditionals
*/
import java x. swing.*;
File: J OPConditional.ja va
public cla ss J OPConditional {
}
public static void m ain( String[ ] arg s ) {
int answe r = JOp tionPane.showConfirmDialog( null, "I sn't J ava g rea t?" );
if (answe r == JOptionPane.YES_ OPTI ON )
JOp tionPane.sho wMe ssageDialog( null, " Wise c hoice." );
else
JOp tionPane.sho wMe ssageDialog( null, " Wrong an swer." );
System. exit(0 );
}
27
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 28
Another Example of Conditionals
File: Simple Te st.ja va
/**
* A simple intelligence te st
*/
import java x. swing.*;
public cla ss Simple Te st {
public static void main( String[ ] a rgs ) {
String choice = JOptionPane.showInputDialog (
" What is the world's g rea test university? (hint: U MCP)" );
if ( choice.equals( “U MCP” ) )
// correct respon se
J OptionPane.showM essageDialog ( null, “Wi se choice.” );
e lse
// incorrect re sponse
J OptionPane.showM essageDialog ( null, “So rry, you blew it. ” );
Sy stem.e xit(0);
// terminate the program
}
}
28
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 29
while Loop Example
Task:
int x = 10;
while ( x >= 0 ) {
System.out.println( x + “ bottles of beer on the wall” );
x = x-1;
}
System.out.println( “Done” );
Output:
29
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 30
Example of Loops and Conditionals
File: Simple Test2.java
/**
* A simple intelligence test (with a correctness check)
*/
import javax.swing.*;
public class Simp leTe st2 {
public static void main( String[ ] a rgs ) {
boolean isCorrect;
do {
String choice = JOptionPane.showInputDialog(
“What is the world' s grea test unive rsity? (hint: UMCP)” );
if ( choice.equals( “UMCP” ) ) {
// correct response
isCorrect = true;
} else {
// incorrect response
isCorrect = false;
JOptionPane.showMessageDialog( null, “You ble w it. Try again.” );
}
} while ( ! isCorrect );
// keep trying until correct
}
}
JOptionPane.showMessageDialog( null, “Wise choice.” );
System. exit(0);
// terminate program
30
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 31
Sample
Sample Execution
Execution
isCorrect
isCorrectisisset
set to
to true
true
and
andso
so loop
loopexits
exits
31
31
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 32
Constants (Literals)
Specifying constants:
Integer Types:
byte
short
int
long
Floating-Point Types:
double
Decimal notation:
Scientific notation:
float
32
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 33
Character and String Constants
char constants:
– letters and digits:
– punctuation symbols:
– escape sequences:
String constants:
Escape sequences:
\” double quote
\’ single quote
\\ backslash
\n new-line character (start a new line)
\t tab character
Examples:
33
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 34
Variable Names
Recall:
– Java’s primitive types: boolean, char, byte, short, int, long, float,
double.
Valid Variable Names: These rules apply to all Java names, or
identifiers, including methods and class names.
– Starts with: a letter (a-z or A-Z), dollar sign ($), or underscore
(_).
– Followed by: zero or more letters, dollar signs, underscores, or
digits (0-9).
– Uppercase and lowercase are different (total ≠ Total ≠ TOTAL).
– Cannot be any of the reserved names. These are special names
(keywords) reserved for the compiler. Examples:
class, float, int, if, then, else, do, public, private, void, …
See page 35 in Lewis and Loftus for a complete listing.
34
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 35
Variable Name Conventions
Naming Conventions: Conventions tha t have developed over time.
Variables and methods:
Class names:
Named constants
35
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 36
Short-Circuiting
Short-circuiting in Logical Operators:.
Why is this useful?
Also works with ||:
36
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 37
Operator Precedence
Operator Precedence:
Unary ops: +x, -x, ++x, --x, x++, x-- , !x
Multiplicative ops: *, /, %
Addition/Subtraction: +, Comparisons: <, <=, >, >=
Equality: ==, !=
Logical ops: &&, || (&& is higher than ||)
Assignments: =, +=, -=, *=, /=, etc.
Example:
if ( 2 * x ++ < 5 * z + 3 && - w != x / 2 * y ) …
Equivalent:
if ( ( (2*(x ++)) < ((5*z) + 3) ) && ((-w) != ((x /2)*y)) ) …
37
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 38
Type Casting
Casting:
Automatic (Implicit) Casting:
double  float  long  int  short  byte
38
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 39
Type Casting
Automatic Casting Examples:
int intVar = 12;
double doubleVar = 5;
long longVar = intVar;
int intVar2 = longVar;
float floatVar1 = 2.3;
float floatVar2 = 2.3f;
intVar2 = 2.0 * intVar;
39
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 40
Explicit Casting
Someti mes you need to cast one numeric type to another:
Explicit cast: Converts one numeric type explicitly into another.
(  desired type )  expression
Example 1: Avoid truncation from integer division.
int x = 23; int y = 4;
double d = x / y;
double e = (double) x / (double) y;
Example 2:
int degreesCelsius = … ;
int degreesFahrenheit = (int) ( ( 9.0 / 5.0 ) * degreesCelsius ) + 32.0 );
40
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 41
Objects
Object:
State:
Behavior:
Examples:
Bank account:
State:
Behaviors:
Voice-mail system:
State:
Behaviors:
Object-oriented programming:
41
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 42
Classes
Class:
Instance Data:
Methods:
Example: Bank account
Instance data:
String accountNumber;
String ownersName;
String ownersAddress;
double currentBalance;
Methods:
debit: decrease the current balance by a given amount
credit: increase the current balance by a given amount
addInterest: compute interest and add it to the balance
...
Encapsulation:
42
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 43
Creating Objects
Primitive type value:
Reference to an object:
Variable declaration:
Primitive types:
Class object:
Examples:
int x = 52;
String s = new String( “Schultzie” );
String t = “von Wienerschnitzel”;
x
s
52
Schultzie
t
von Wienerschnitzel
43
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 44
Under the Hood: What does “new ” do?
Wha t happens when “new” is called:
String s = new String( “Schultzie” );
String t = new String( “von Wienerschnitzel” );
x
s
52
the Heap
Schultzie
t
von Wienerschnitzel
44
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 45
The Java Class Library
Java’s class library:
java.lang:
java.util:
Note:
‘x’
java.text:
java.awt:
javax.swing:
java.io:
java.applet:
See also Appendix M in L&L and Sun’s Java API Specs (a link can be
found in the Resources class web page).
45
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 46
Accessing the Class Library
Fully qualified name:
Example:
javax.swing.JOptionPane.showMe ssageDialog( null, “ This is really inconvenient!” );
String input = javax.swing.JOptionPane.showInputDialog( “I agree!” );
46
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 47
The Import Statement
Import Statement:
import javax.swing.JOptionPane;
// import class JOptionPane
…
// no need for “javax.swing” anymore
String input = JOptionPane.showInputDialog( “Much better” );
Importing All the Classes:
import java.util.*;
// import all classes from java.util
import javax.swing.*;// import all classes from javax.swing
java.lang:
47
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 48
JOptionPane - Revisited
JOptionPane:
JOptionPane showConfirmDialog( null,
“Your prompt here”,
“Window title here”,
optionType);
// (always null for us)
// prompt for the user
// title for the window
// what options to give the use r
Example:
JOptionPane showConfirmDialog( null,
“Are you sure you want to quit?\nI mean really su re?”,
“Confirm Quit”,
JOptionPane.YES_NO_OPTION);
48
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 49
The String Class - Revisited
Let:
String s = new String( “Schultzie” );
String t = new String( “sCHultZIE” );
Length:
int i = s.length( );
Comparisons:
boolean a = s.equals( t );
boolean b = s.equalsIgnoreCase( t );
int j = s.compareTo( t );
int k = s.compareToIgnoreCase( t );
Access character at a given index: (index runs from 0 to length-1)
char c = s.charAt( 0 );
char d = s.charAt( 2 );
Change Case:
String x = t.toLowerCa se( );
String y = t.toUpperCase( );
(See Page 89 in L&L for more examples.)
49
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 50
The NumberFormat Class
NumberFormat:
Import: import java.text.*;
Currency Conversion:
NumberFormat money = NumberFormat.getCurrencyInstance( );
double amount = 123.6;
System.out.println( money.format(amount) );
Percentage Conversion:
NumberFormat percent = NumberFormat.getPercentInstance( );
double taxRate = 0.0793;
System.out.println( percent.format(taxRate) );
50
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 51
Example of Currency Conversion
/* This is a simple cashie r checkout program */
import java.text.*;
import javax.swing.*;
public class Cashier {
public static void main( String[ ] a rgs ) {
double priceOfMilk = 3.50;
// item prices
double priceOfSugar = 1.25;
double total = 0.0;
// initialize total price
String item;
do {
// read items until 'quit'
item = JOptionPane.showInputDialog( "Enter Item (or 'quit') " );
if ( item.equals( "milk" ) )
total += priceOfMilk;
else if ( item.equals( "sugar" ) )
total += priceOfSugar;
} while ( ! item.equals( "quit" ) );
// convert to currency
NumberFormat money = NumberFormat.ge tCurrencyInstance( );
JOptionPane.showMessageDialog( null, "Amount Due: " + money.format( total ) );
System. exit( 0 );
}
}
51
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 52
Under
Under the
the Hood:
Hood: Objects
Objects vs.
vs. Primitive
Primitive Types
Types
Technical
Technical Question:
Question:Why
Whydoes
doesJava
Javatrea
treattpri
primi
mitive
tive types
typesand
and
objects
objectsdifferently?
differently?
String
String ss == “S
“Schultzie
chultzie”;”;
ss == “this
“this might
might be
be aa ridiculously
ridiculously long
long string…”;
string…”;
xx
ss
tt
52
52
the
theHeap
Heap
Schultzie
Schultzie
this
thismight
mightbe…
be…
von
vonWienerschnitzel
Wienerschnitzel
52
52
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 53
Under the Hood: Assignment and Aliasing
Remem ber: Java allows Strings
to be tre ate d “a lmost” a s if
they we re primitive type s.
Just for Strings:
String t = “von Wienerschnitzel”;
is convenient shorthand for what Ja va really does:
String t = new String( “von Wienerschnitzel” );
Aliasing: When one objec t referenc e is assigned to another, the
memory address is copied, but not the objec t i tself. To crea te a
new instance requires a call to “new”.
String u = t;
String w = new String( t );
// copies the address (reference)
// creates a new string initialized to t
The variable u is effec tively an
alias for t, tha t is, a different na me
for the sa me objec t.
Beware: Aliasing is considered
dangerous, since changing one
variable can modify another.
the H eap
t
von Wiene rschnitz el
u
w
von Wiene rschnitz el
53
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 54
Under the Hood: ‘==’ and ‘equals’ Revisited
Start with the ini tializations:
String t = new String( “von Wienerschnitzel” );
String u = t;
// copies the reference (address)
String w = new String( t ); // creates a new string initialized to t
Consider now the differenc e between == and equals( ) .
==: Tests whet her the references (addresses) are equal.
equals( ): Tests whether the contents are equal.
if ( u == t ) …
if ( w == t ) …
if ( u.equals(w) )
// true: u and t refer to the same object
// false: w and t refer to different objects
// true: u’s and w’s contents are equal
Bottom line: Applying == to strings i s
legal, but it al most never achieves
the result you intended. Use
equals( ) instead.
the H eap
t
von Wiene rschnitz el
u
w
von Wiene rschnitz el
54
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 55
Under the Hood: ‘==’ and ‘equals’ Revisited
Start with the ini tializations:
String t = new String( “von Wienerschnitzel” );
String u = t;
String w = new String( t );
Consider now the differenc e between == and equals( ) .
==: .
equals( ):
if ( u == t ) …
if ( w == t ) …
if ( u.equals(w) )
Bottom line:
the H eap
t
von Wiene rschnitz el
u
w
von Wiene rschnitz el
55
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 56
Under the Hood: Garbage Collection
Garbage:
int x = 52;
String s = new String( “Schultzie” );
String t = new String( “von Wienerschnitzel” );
s = new String( “Another string” );
Garbage Collection:
x
s
t
52
the Heap
Schultzie
Another string
von Wienerschnitzel
56
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 57
Program Development
How do I build a program?
Software development lifecycle:
Analysis:
Design:
Implementation:
Testing:
Maintenance:
The “cycle”:.
57
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 58
Anatomy of a Class
A class contains declarations of:
Instance data:
Methods:
Typical class file structure:
public class Widget {
int dataItem1;
double dataItem2;
String dataIterm3;
File: Widget.ja va
methodDefinition1(…) {
…
}
Declaration of instance data
Declaration of methods
methodDefinition2(…) {
…
}
}
58
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
Slide 59
Example: Date
Instance Data:
int month:
int day:
int year:
Ranges from 1 to 12 (e.g. 1 = Jan, 2 = Feb, etc)
Ranges from 1 to 31 (depending on the month)
Four digit year (e.g. 2004)
Methods:
Date( int m, int d, int y ):
toString( ):
equals( Date d ):
60
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 60
Example: Date.java (part 1)
/*
* Date: An object that sto res a date
*/
File: Date.java (pa rt 1)
public class Date {
private int month;
private int day;
private int year;
// the month (from 1-12)
// the day of the month (1-31)
// the year (four digits)
/* Constructor method initializes a new Date object */
public Date( int m, int d, int y ) {
month = m; day = d; year = y;
}
}
// (insert part 2 here)
61
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 61
Creating a Date Object
A Date object is created using “new”:
Date indepDay = new Date( 7, 4, 1776 );
// July, 4, 1776
This generates a call
to the constructor:
public Date( int m, int d, int y ) {
month = m; day = d; year = y;
}
62
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 62
Example: Date.java (part 2)
This goes inside the Date cla ss
File: Date.java (pa rt 2)
/* Converts to a string */
public String toString( ) {
return new String( month + "/" + day + "/" + year );
}
/* Is this date equal to anothe r? */
public boolean equals( Date d ) {
if ( ( year == d.year ) && ( month == d.month ) && ( da y == d.day ) )
return true;
else
return false;
}
63
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 63
Using the “ toString” method
Printing a Date object:
Date indepDay = new Date( 7, 4, 1776 );
// July, 4, 1776
System.out.println( “Independence day is ” + indepDay.toString( ) );
public String toString( ) {
return new String( month + "/" + day + "/" + year );
}
Output: Independence day is 7/4/1776
System.out.println( “Independence day is ” + indepDay);
64
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 64
Using the “equals” method
Comparing two dates:
Date bobsBirthday = new Date( 7, 18, 1985 ); // July 18, 1985
Date carolsBirthday = new Date( 3, 23, 1985 ); // March 23, 1985
if ( bobsBirthday.equals( carolsBirthday ) ) …
// (false)
This invokes Bob’s equals method:
public boolean equals( Date d ) {
if ( ( year == d.year ) && ( month == d.month ) && ( da y == d.day ) )
return true;
else
return false;
}
Carol’s birthday is the actual parameter. It is substi tuted for the
formal parameter “d” in the method.
65
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 65
Example: DateDemo.java
/* This file demos the Date cla ss */
File: DateDemo.java
public class DateDemo {
public static void main( String[ ] a rgs ) {
Date bobsBirthday = new Date( 7, 18, 1985 );
Date carolsBirthday = new Date( 3, 23, 1985 );
// July 18, 1985
// March 23, 1985
System.out.p rintln( "His birthday is " + bo bsBirthday.toString( ) );
System.out.p rintln( "He r birthday is " + carolsBirthday. toString( ) );
}
}
if ( bobsBirthday. equals( ca rolsBirthday ) )
System.out.p rintln( "Sa me birthday" );
else
System.out.p rintln( "Different birthdays" );
Output:
His birthday i s 7/18/1985
Her birthday is 3/23/1985
Different birthdays
66
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 66
Visibility and Encapsulation
Two views of an object:
Class user (client): sees the public interface,
Class implementer: sees all the class’s data and methods.
.
Visibility Modifiers: Control how members
can be accessed.
private:
public:.
[protected]:.
67
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 67
Visibility and Encapsulation
Example:
File: Modifiers.java
public class Modifiers {
public int pubData;
private int privData;
public void pubMethod( ) { /* omitted */ }
private void privM ethod( ) { /* omitted */ }
}
public class ModifierDemo {
public static void main( String[ ] args ) {
Modifiers mod = new Modifiers( );
mod.pubData = 1;
mod.pubM ethod( );
mod.privData = 1;
mod.privMethod( );
}
}
File: ModifierDemo.java
68
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 68
Visibility: Guidelines
Wha t should be visible and what not?
Instance data should be private:
Example: month could reasonably be any of the following…
int from 1-12:
int from 0-11:
String: “Jan”, “Feb”,
Exception: Constants can be made public.
public final int DAYS_PER_WEEK = 7;
69
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 69
Visibility: Guidelines
Wha t should be visible and what not?
Methods in the public interface are public:
Utility/Support methods should be private:
Conventions: Methods are often further distinguished by their
general function.
Accessors:
Mutators:.
Examples: Possible additional methods for the Date class:
Accessor:
Mutator:
int getMonth( ) { return month; }
void incrementYear( ) { year++; }
70
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________
Slide 70
Method Return Types and “void”
A method can either:
Return a value:.
Return no value:.
Examples: (Parameters and method bodies omitted)
public String toString( )
public boolean equals( … )
private double getPressure( … )
public void printHelp( )
private void changeAddress( … )
71
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
____________________________________________________________________