Primitive Types,
Strings, and Console I/O
 Variables and Expressions
 The Class String
 Keyboard and Screen I/O
 Documentation and Style
Reading => Section 1.2
1.1
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Variables and Values
 Variables are memory locations that store data such as numbers and letters.
 The data stored by a variable is called its value.
 The value is stored in the memory location.
 A variables value can be changed.
1.2
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Variables and Values
public class EggBasket
Output:
{
If you have
public static void main (String[] args)
6 eggs per basket and
{
10 baskets, then
int numberOfBaskets, eggsPerBasket, totalEggs;
the total number of eggs is 60
numberOfBaskets = 10;
eggsPerBasket = 6;
totalEggs = numberOfBaskets * eggsPerBasket;
System.out.println ("If you have");
System.out.println (eggsPerBasket + " eggs per basket and");
System.out.println (numberOfBaskets + " baskets, then");
System.out.println ("the total number of eggs is " + totalEggs);
}
}
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Variables and Values
 Variables:
numberOfBaskets
eggsPerBasket
totalEggs
 Assigning values:
numberOfBaskets = 10;
eggsPerBasket = 6;
totalEggs = numberOfBaskets * eggsPerBasket;
 A variable must be declared before it is used.
 When you declare a variable, you provide its name and type.
int numberOfBaskets, eggsPerBasket, totalEggs;
 A variable’s type determines what kinds of values it can hold, e.g.,
integers, real numbers, characters.
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Syntax and Examples
 Variable declaration syntax:
type variable_1, variable_2, …;
 Examples:
int styleChoice, numberOfChecks;
double balance, interestRate;
char jointOrIndividual;
 A variable is declared just before it is used or at the beginning of a
“block” enclosed in { }:
public static void main(String[] args)
{
/* declare variables here */
:
}
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Types in Java
 In most programming languages, a type implies several things:
 A set of values
 A (hardware) representation for those values
 A set of operations on those values
 Example - type int:
 Values – integers in the range -2147483648 to 2147483647
 Representation – 4 bytes, binary, “two’s complement”
 Operations – addition (+), subtraction (-), multiplication (*), division (/), etc.
 Two kinds of types:
 Primitive types
 Class types
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Types in Java
 A primitive type:
 values are “simple,” non-decomposable values such as an individual number
or individual character
 int, double, char
 A class type:
 values are “complex” objects
 a class of objects has both data and methods
 “Think WHIRLED peas.” is a value of class type String
 ‘November 10, 1989’ is a value of class type date (non-Java)
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Java Identifiers
 An identifier:
 a name given to something in a program
 name of a variable, name of a method, name of a class, etc.
 created by the programmer, generally
 Identifiers may contain only:
 letters
 digits (0 through 9)
 the underscore character (_)
 and the dollar sign symbol ($) which has a special meaning
 the first character cannot be a digit.
 Identifiers may not contain any spaces, dots (.), asterisks (*), or other
characters not mentioned above:
7-11
netscape.com
util.*
1.8
(not allowed)
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Java Identifiers, cont.
 Java is case sensitive i.e., stuff, Stuff, and STUFF are different
identifiers.
 keywords or reserved words have special, predefined meanings:
abstract assert boolean break byte case catch char class const
continue default do double else enum extends false final finally
float for goto if implements import instanceof int interface long
native new null package private protected public return short
static strictfp super switch synchronized this throw throws
transient true try void volatile while
 Keywords cannot be used as identifiers
 Identifiers can be arbitrarily long.
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Naming Conventions
 Choose names that are helpful, or rather readable, such as count or
speed, but not c or s.
 Class types:
 begin with an uppercase letter (e.g. String).
 Primitive types:
 begin with a lowercase letter (e.g. int).
 Variables of both class and primitive types:
 begin with a lowercase letters (e.g. myName, myBalance).
 multiword names are “punctuated” using uppercase letters.
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Primitive Types
 Four integer types:
 byte
 short
 int (most common)
 long
 Two floating-point types:
 float
 double (most common)
 One character type:
 char
 One boolean type:
 boolean
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Primitive Types, cont.
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Examples of Primitive Values
 Integer values:
0
-1
365
12000
 Floating-point values:
0.99
-22.8
3.14159 5.0
 Character values:
`a`
`A`
`#`
` `
 Boolean values:
true
false
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Motivation for Primitive Types
 Why are there several different integer types?
 storage space
 operator efficiency
 More generally, why are there different types at all?
 reflects how people understand different kinds of data, e.g., letter vs.
numeric grades.
 helps prevent programmer errors.
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Assignment Statements
 An assignment statement is used to assign a value to a variable:
int answer;
answer = 42;
 The “equal sign” is called the assignment operator.
 In the above example, the variable named answer is assigned a value
of 42, or more simply, answer is assigned 42.
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Assignment Statements, cont.
 Assignment syntax:
variable = expression ;
where expression can be
 a literal or constant (such as a number),
 another variable, or
 an expression which combines variables and literals using operators
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Assignment Examples
 Examples:
int amount;
int score, numberOfCards, handicap;
int eggsPerBasket;
char firstInitial;
:
amount = 3;
firstInitial = ‘W’;
score = numberOfCards + handicap;
eggsPerBasket = eggsPerBasket - 2;
=> last line looks weird in mathematics, why?
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Assignment Evaluation
 The expression on the right-hand side of the assignment operator (=) is
evaluated first.
 The result is used to set the value of the variable on the left-hand side of
the assignment operator.
score = numberOfCards + handicap;
eggsPerBasket = eggsPerBasket - 2;
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Simple Screen Output
 The following outputs the String literal “The count is “ followed by the
current value of the variable count.
System.out.println(“The count is “ + count);
 “+” means concatenation if at least one argument is a string
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Simple Input
 Sometimes data is needed and obtained from the user at run time.
 Simple keyboard input requires:
import java.util.*;
or
import java.util.Scanner;
at the beginning of the file.
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Simple Input, cont.
 A “Scanner” object must be initialized before inputting data:
Scanner keyboard = new Scanner(System.in);
 To input data:
eggsPerBasket = keyboard.nextInt();
which reads one int value from the keyboard and assigns it to the
variable eggsPerBasket.
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Simple Input, cont.
 class EggBasket2
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Command-Line Arguments
 Frequently input is provided to a program at the command-line.
public class UseArgument
{
public static void main(String[] args)
{
System.out.print(“Hi, ”);
System.out.print(args[0]);
System.out.println(“. How are you?”);
}
}
 Sample interaction:
% javac UseArgument.java
% java UseArgument Alice
Hi, Alice. How are you?
% java UseArgument Bob
Hi, Bob. How are you?
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Command-Line Arguments
 Frequently multiple values are provided at the command-line.
public class Use3Arguments
{
public static void main(String[] args)
{
System.out.print(“The first word is ”);
System.out.print(args[0]);
System.out.print(“, the second is ”);
System.out.print(args[1]);
System.out.print(“, and the third is ”);
System.out.println(args[2]);
}
}
 Sample interaction:
% javac Use3Arguments.java
% java Use3Arguments dog cat cow
The first word is dog, the second is cat, and the third is cow
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Command-Line Arguments
 Command-line arguments can be numeric.
public class IntOps {
public static void main(String[] args) {
int a = Integer.parseInt(args[0]);
// Notice the variable declaration
int b = Integer.parseInt(args[1]);
// Notice the comments…lol
int sum
= a + b;
int prod = a * b;
int quot = a / b;
int rem
= a % b;
System.out.println(a + " + " + b + " = " + sum);
System.out.println(a + " * " + b + " = " + prod);
System.out.println(a + " / " + b + " = " + quot);
System.out.println(a + " % " + b + " = " + rem);
}
}
 Sample interaction:
% javac IntOps.java
% java IntOps 1234 99
1234 + 99 = 1333
1234 * 99 = 122166
1234 / 99 = 12
1234 % 99 = 46
1.25
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Literals
 Values such as 2, 3.7, or ’y’ are called constants or literals.
 Integer literals can be preceded by a + or - sign, but cannot contain
commas.
 There are two distinct properties that every integer literal has:
 format – either decimal, hexadecimal or octal, and
 type – either long or int
 Both the format and the type of an integer literal can be determined
by…looking at it!
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Integer Literal Formats
 Decimal:
 0, 10, 37, 643, 829, etc.
 first digit must NOT be zero, for any non-zero integer
 Hexadecimal:
 consists of the leading characters 0x or 0X followed by one or more
hexadecimal digits, i.e., 0 through F (lower and upper case equivalent)
 each letter may be either upper case or lower case
 0xA (decimal 10), 0x0 (decimal 0), 0xFF (decimal 255), 0xf0 (decimal 240),
0x34A2, 0Xff decimal (255), etc.
 Octal:
 Consists of the leading digit 0 followed by one or more octal digits, i.e., 0
through 7
 010 (decimal 8), 023 (decimal 19), 037 (decimal 31)
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Integer Literal Formats
 What is the format?
 0
 2
 0372
 0xDadaCafe
 1996
 0x00FF00FF
 0A3C
 0945
 450xA
1.28
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Integer Literal Formats
 The format used to specify an integer literal has no impact on its
corresponding internal value.
 All of the following println statements output the same thing:
int x;
x = 16;
System.out.println("Value:" + x);
x = 020;
System.out.println("Value:" + x);
x = 0x10;
System.out.println("Value:" + x);
1.29
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Integer Literal Type
 An integer literal is of type long if it is suffixed with an letter L or l;
otherwise it is of type int.
 note that capital L is preferred
 Integer literals of type long:
 2L
 0372L
 0xDadaCafeL
 1996L
 0x00FF00FFL
 0l
 0777L
 0x100000000l
 2147483648L
 0xC0B0L
1.30
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Integer Literal Type
 See the program:
 http://www.cs.fit.edu/~pbernhar/teaching/cse1001/literals
1.31
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Floating Point Literals
 Just like with integer literals…
 Floating point literals can also be preceded by a + or - sign, but cannot
contain commas.
 There are two distinct properties that every floating point literal has:
 format – either fully expanded notation or scientific notation
 type – either float or double
 Both the format and the type of a floating point literal can be determined
by…looking at it!
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Floating Point Literal Formats
 Floating-point constants can be written:
 with digits after a decimal point, as in 3.5 or
 using scientific notation
 Examples:
 865000000.0 can be written as 8.65e8
 0.000483 can be written as 4.83e-4
 The number in front of the “e” does not need to contain a decimal point,
e.g. 4e-4
1.33
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Floating Point Literal Type
 An floating point literal is of type float if it is suffixed with an letter F or f;
otherwise it is of type double.
 Floating point literals of type float:
 2.5F
 0.0f
 8.65e8f
 4e-4F
 3f
 +35.4f
 -16F
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Assignment Compatibilities
 Java is said to be strongly typed, which means that there are limitations on
mixing variables and values in expressions and assignments.
int x = 0;
long y = 0;
float z = 0.0f;
x
x
y
z
y
=
=
=
=
=
y;
z;
z;
3.6;
25;
//
//
//
//
//
illegal
illegal
illegal
illegal (3.6 is of type double)
legal, but interesting…
1.35
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Assignment Compatibilities
 Sometimes automatic conversions between types do take place:
short s;
int x;
s = 83;
x = s;
double doubleVariable;
int intVariable;
intVariable = 7;
doubleVariable = intVariable;
1.36
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Assignment Compatibilities, cont.
 A value of one numeric type can be assigned to a variable of any type
further to the right, as follows:
byte --> short --> int --> long --> float --> double
but not to a variable of any type further to the left.
 Makes sense intuitively because, for example, any legal byte value is a
legal short value.
 On the other hand, many legal short values are not legal byte values.
1.37
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Assignment Compatibilities, cont.
 Example – all of the following are legal, and will compile:
byte b;
short s;
int i;
long l;
float f;
double d;
b = 10;
s = b;
i = b;
l = i;
f = l;
// This one is interesting, why?
d = f;
1.38
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Assignment Compatibilities, cont.
 Example – NONE (except the first) of the following will compile:
byte b;
short s;
int i;
long l;
float f;
double d;
d = 1.0;
f = d;
l = f;
i = l;
s = i;
b = s;
1.39
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Type Casting
 A type cast creates a value in a new type from an original type.
 A type cast can be used to force an assignment when otherwise it would
be illegal (thereby over-riding the compiler, in a sense).
 Example:
double distance;
distance = 9.0;
int points;
points = (int)distance;
 The above would be illegal without (int).
1.40
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Type Casting, cont.
 The value of (int)distance is 9, but the value of distance, both
before and after the cast, is 9.0.
 The type of distance does NOT change and remains double.
 What happens if distance contains 9.7?
 Any nonzero value to the right of the decimal point is truncated (as oppossed
to rounded).
 Remember the rule – “cast with care,” because the results can be
unpredictable.
1.41
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Characters as Integers
 Like everything else, each character is represented by a binary sequence.
 The binary sequence corresponding to a character is a positive integer.
 Which integer corresponds to each character is dictated by a standardized
character encoding.
 each character is assigned a unique integer code
 the codes are different for upper and lower case letters, e.g., 97 may be the
integer value for ‘a’ and 65 for ‘A’
 some characters are printable, others are not
 Why should different computers use the same code?
 ASCII and Unicode are common character codes
1.42
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Unicode Character Set
 Most programming languages use the ASCII character encoding.

American Standard Code for Information Interchange (ASCII)

(only) encodes characters from the north American keyboard

uses one byte of storage
 Java uses the Unicode character encoding which includes ASCII.
 The Unicode character set:
 uses two bytes of storage
 includes characters from many different alphabets other than English (in
contrast to ASCII)
 codes characters from the North American keyboard the same way that
ASCII does
1.43
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ASCII/Unicode
32
48
0
…
33
34
35
36
37
38
39
40
41
!
“
#
$
%
&
‘
(
)
57
9
…
65
…
A
90
Z
1.44
…
97
a
…
122
z
©Silberschatz, Korth and Sudarshan
Assigning a char to an int
 A value of type char can be assigned to a variable of type int to obtain
its Unicode value.
 Example:
char answer = ’y’;
System.out.println(answer);
System.out.println((int)answer);
>y
>121
 See the program at:
http://www.cs.fit.edu/~pbernhar/teaching/cse1001/charTest
1.45
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Initializing Variables
 A variable that has been declared, but not yet given a value is said to be
uninitialized.
int x, y, z;
x = y;
x = z + 1;
 Some languages automatically initialize a variable when it’s declared,
other languages don’t.
 Others (Java) initialize in some circumstances, but not in others.
 Variables declared to be of a primitive type are NOT automatically initialized.
 In other cases Java will initialize variables; this will be discussed later.
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Initializing Variables
 Some languages report an error when a variable is used prior to
initialization by the program.
 Sometimes at compile time, other times at run-time.
 Some languages won’t report an error, and will even let you use an
uninitialized variable.
 In such cases the initial value of the variable is arbitrary!
 The program might appear to run correctly sometimes, but give errors on
others.
 Java:
 The compiler will (try) to catch uninitialized variables.
=> Always make sure your variables are initialized prior to use!
1.47
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Initializing Variables, cont.
 In Java, a variable can be assigned an initial value in it’s declaration.
 Examples:
int count = 0;
char grade = ’A’;
// default is an A
 Syntax:
type variable1 = expression1, variable2 = expression2, …;
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Arithmetic Operations
 Arithmetic expressions:
 are formed using the +,
-, *, / and %
operators
 operators have operands, which are literals, variables or sub-expressions.
 Expressions with two or more operators can be viewed as a series of
steps, each involving only two operands.
 The result of one step produces an operand which is used in the next step.
 Note that Java is left-associative.
 Example:
int x = 0, y = 50, z = 20;
double balance = 50.25, rate = 0.05;
x = x + y + z;
balance = balance + (balance * rate)
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Expression Type
 An arithmetic expression can have operands of different numeric types.
 x + (y * z) / w
 Note that this does not contradict our rules for assignment.
 Every arithmetic expression has a (resulting) type.
 Given an arithmetic expression:
 If any operand in the expression is of type double, then the expression has
type double.
 Otherwise, if any operand in the expression is of type float, then the
expression has type float.
 Otherwise, if any operand in the expression is of type long, then the
expression has type long.
 Otherwise the expression has type int.
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Expression Type, cont.
 Example:
int hoursWorked
= 40;
double payRate
= 8.25;
double totalPay;
Then the expression in the assignment:
totalPay = hoursWorked * payRate
is a double with a value of 500.0.
1.51
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Operators with integer
and floating point numbers
 See the program:
 http://www.cs.fit.edu/~pbernhar/teaching/cse1001/expressions
 http://www.cs.fit.edu/~pbernhar/teaching/cse1001/integralConversion
1.52
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The Division Operator
 The division operator (/) behaves as expected.
 If one of the operands is a floating-point type then the result is of the
same floating point type.
 9.0 / 2 = 4.5
 9 / 2.0 = 4.5
 If both operands are integer types then the result is truncated, not
rounded.

9/2 = 4

99 / 100 = 0
1.53
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The mod Operator
 The mod (%) operator is used with operands of integer type to obtain the
remainder after integer division.
 14 divided by 4 is 3 with a remainder of 2.
 Hence, 14 % 4 is equal to 2.
 The mod operator has many uses, including determining:
 If an integer is odd or even (x % 2 = 0)
 If one integer is evenly divisible by another integer (a % b = 0)
1.54
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Case Study: Vending Machine Change
 Program Requirements:
 The user enters an amount between 1 cent and 99 cents.
 The program determines a combination of coins equal to that amount.
 For example, 55 cents can be two quarters and one nickel.
=> What are “requirements” anyway?
 Sample dialog:
Enter a whole number from 1 to 99.
The machine will determine a combination of coins.
87
87 cents in coins:
3 quarters
1 dime
0 nickels
2 pennies
1.55
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Case Study, cont.
 Algorithm (version #1, in pseudo-code):
1. Read the amount.
2. Find the maximum number of quarters in the amount.
3. Subtract the value of the quarters from the amount.
4. Repeat the last two steps for dimes, nickels, and pennies.
5. Print the amount and the quantities of each coin.
=> What is an “algorithm” anyway?
=> What is “pseudo-code” also?
 Program Variables Needed:
int amount, quarters, dimes, nickels, pennies;
1.56
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Case Study,cont.
 Interpreted literally, the algorithm doesn’t work properly, because the
original amount is changed by the intermediate steps.
 The original value of amount is lost.
 Add an additional variable:
int amount, originalAmount, quarters, dimes,
nickles, pennies;
and update the algorithm.
1.57
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Case Study, cont.
 Algorithm (version #2):

1.
Read the amount.
2.
Make a copy of the amount.
3.
Find the maximum number of quarters in the amount.
4.
Subtract the value of the quarters from the amount.
5.
Repeat the last two steps for dimes, nickels, and pennies.
6.
Print the original amount and the quantities of each coin.
Typically pseudo-code is iteratively embellished or enhanced.
1.58
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Case Study, cont.
 How do we determine the number of quarters in an amount?
 There are 2 quarters in 55 cents, but there are also 2 quarters in 65 cents.
 That’s because 55 / 25 = 2 and 65 / 25 = 2.
 How do we determine the remaining amount?
 Using the mod operator:
55 % 25 = 5 and 65 % 25 = 15
 Similarly for dimes, nickels and pennies
 Pennies are simply amount % 5.
1.59
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Case Study, cont.
1.60
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Case Study—testing the implementation
 The program should be tested with several different amounts.
 Test with values that give zero values for each possible coin
denomination.
 Test with amounts close to:
 “Extreme” or “boundary condition” values such as 0, 1, 98 and 99.
 Coin denominations such as 24, 25, and 26.
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Increment (and Decrement) Operators
 Used to increase (or decrease) the value of a variable by 1.
 count = count +1
 count = count -1
 Easy to use, important to recognize.
 The increment operator:
 count++
 ++count
 The decrement operator:
 count- --count
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Increment (and Decrement) Operators
 “Mostly” equivalent operations:
count++;
++count;
count = count + 1;
count--;
--count;
count = count - 1;
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Increment (and Decrement)
Operators in Expressions
 After executing:
int m = 4;
int result = 3 * (++m);
result has a value of 15 and m has a value of 5
 After executing:
int m = 4;
int result = 3 * (m++);
result has a value of 12 and m has a value of 5
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Increment and Decrement Operator, Cont.
 Common code:
int n = 3;
int m = 4;
int result;
 What will be the value of m and result after each of these executes?
(a) result = n * ++m;
(b) result = n * m++;
(c) result = n * --m;
(d) result = n * m--;
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Precedence Rules—Binary Operators
 An expression (without parenthesis) is evaluated according to the
(basic) rules of precedence:
 Highest precedence – unary operators +, -, ++, -- and !
 Intermediate precedence – binary arithmetic operators *, / and %
 Lowest precedence – binary arithmetic operators + and  Binary operators in Java are “left-associative:”
 When binary operators have equal precedence the operator on the left has
higher precedence than the operator(s) on the right.
 Unary operators in Java are “right-associative:”
 When unary operators have equal precedence the operator on the right has
higher precedence
 if x contains 10
-++x is -11 and x is 11 afterwards; same as –(++x)
• -x++ is -10 and x is 11 afterwards; same as –(x++)
•
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Use Parentheses
 Parentheses can be used to over-ride the rules of precedence:
(cost + tax) * discount
 Parenthesis can also be used to clarify code, even when precedence is
not over-ridden:
balance + (interestRate * balance)
 Spaces also clarify code:
balance + interestRate*balance
but spaces do not dictate precedence.
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Sample Expressions
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The Class String
 As we already have seen, a String is a sequence of characters.
 We’ve used constants, or rather, literals of type String:
“Enter a whole number from 1 to 99.”
“Number of quarters:”
“I will output a combination of coins”
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Declaring and Printing Strings
 Variables of type String can be declared and Initialized:
String greeting;
greeting = “Hello!”;
 Equivalent to the above:
String greeting = “Hello!”;
String greeting = new String(“Hello!”);
 Printing:
System.out.println(greeting);
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Concatenation of Strings
 Two strings can be concatenated using the + operator:
String greeting = “Hello”;
String name = “Smith”;
String sentence;
sentence = greeting + “ officer ”;
sentence = sentence + name;
System.out.println(sentence);
 Any number of strings can be concatenated using the + operator.
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Concatenating Strings and Integers
 Strings can be concatenated with other types:
String solution;
solution = “The temperature is “ + 72;
System.out.println (solution);
 Output:
The temperature is 72
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Positions in a String
 Each character in a String has its own position.
 Positions are numbered starting at 0.
 ‘J’ in “Java is fun.” is in position 0
 ‘f’ in “Java is fun.” is in position 8
 The position of a character is also referred to as its index.
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Positions in a String, cont.
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Classes
 Recall that Java has primitive types and class types:
 primitive types
 class types
 Primitive types have:
 simple, “atomic,” non-decomposable values
 Operations (built-in)
 Class types have:
 complex values, with structure
 Methods (some built-in, others user-defined)
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Objects, Methods, and Data
 A primitive type is use to create variables.
 A class type is used to produce “objects.”
 An object is an entity that:
 stores data
 can take actions defined by methods
 basically a complex variable.
 The data and methods applicable to an object are defined by its class.
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The Class String
 String is a class type
 The length() method returns an int, which is the number of
characters in a particular String object.
int howMany = solution.length();
 You can use a call to method length() anywhere an int can be used.
int X = 10;
int count = solution.length();
System.out.println(solution.length());
X = X * solution.length() + 3;
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Indexing Characters within a String
using Methods
 charAt(position)
 returns the char at the specified position

Example:
String greeting = "Hi, there!";
char ch1 = greeting.charAt(0);
// Stores ‘H’ in ch1
char ch2 = greeting.charAt(2);
// Stores ‘,’ in ch2
 substring(start, end)
 returns the string from start up to, but not including, end
String myWord;
myWord = greeting.substring(4,7) // Stores the in myWord
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Example of Class String
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String Methods
 See the Java on-line documentation for more details!
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Escape Characters
 How would you print the following?
“Java” refers to a language.
 The following don’t work:
System.out.println(“Java refers to a language.”);
System.out.println(““Java” refers to a language.”);
 The compiler needs to be told that the quotation marks (“) do not signal
the start or end of a string, but instead are to be printed.
System.out.println(“\”Java\” refers to a language.”);
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Escape Characters
 “Escape sequences” are used to print problematic characters.
 Each escape sequence is a single character even though it is written
with two symbols.
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Examples
 Examples:
System.out.println(“abc\\def”);
=>
abc\def
System.out.println(“new\nline”);
=>
new
line
char singleQuote = ‘\’’;
System.out.println(singleQuote);
=>
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Keyboard and Screen
I/O: Outline
 Screen Output
 Keyboard Input
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Screen Output
 We’ve seen several examples of screen output already.
 System.out is an object that is part of Java.
 println() is one of the methods available to the System.out object.
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Screen Output, cont.
 The concatenation operator (+) is useful when everything does not fit on
one line.:
System.out.println(“When everything “ +
“does not fit on one line, use the” +
“ concatenation operator (\’+\’)”);
=> Do not break the line except immediately before or after the concatenation
operator (+).
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Screen Output, cont.
 Alternatively, use print()
System.out.print(“When everything “);
System.out.print(“does not fit on “);
System.out.print(“one line, use the “);
System.out.print(“\”print\” ”);
System.out.println(“statement”);
ending with a println().
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Screen Output, cont.
 Syntax:
System.out.println(output_1 + output_2 + ...+ output_n);
 Example:
System.out.println (1967 + “ “ + “Oldsmobile” + “ “ + 442);
1967 Oldsmobile 442
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printf (or format) Method for Output Formatting

Heavily influenced by C

outputStream.printf(formatString, args…)
 System.out.printf(…)
 smileyOutStream.printf(…)

formatString specifies how to format args

System.out.printf(“%s %d %f%n”, name, id, gpa);
 System.out.println(name + “
“ + id + “ “ + gpa);

Useful for “right justified” numbers

Numbers in println and print are “left justified”
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Formatting String

% width conversion

width specifies how many slots are available for output

If width > number of characters, spaces are printed first before the characters—
“right justified”

printf(“%5d”, count)
 Count
 32901:
 2004:
3
2
9
0
1
 22:
 6747280: all digits are
is ignored
2 printed,
0
0 width
4
2
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Conversion Characters
Conversion
Argument
Description
d
integer
Decimal integer
f
floating point
Decimal float
s
general (String, Boolean, …)
String
n
New line
c
character
Character (unicode)
e
floating point
Decimal scientific notation
o
integer
Octal integer
x
integer
Hexadecimal integer
%
%
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Imprecision in Floating-Point Numbers
 Floating-point numbers often are only approximations since they are
stored with a finite number of bits.
 Hence 1.0/3.0 is slightly less than 1/3.
 1.0/3.0 + 1.0/3.0 + 1.0/3.0 could be less than 1.
 See the program:
 http://www.cs.fit.edu/~pbernhar/teaching/cse1001/floatTest
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Floating-point Precision

width.precision conversion

printf(“%5.2f”, PI)

printf(“%7.4f”, PI)
3
3
.
.
1
1
4
4
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Left Justified

Spaces are added (padded) on the right

Minus (-) sign before the width

…printf(“%-7s %-4d”, name, age)

Why are there
spaces
J 4o
h after
n “John” instead of 3?
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2
0
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Example
 http://www.cs.fit.edu/~pkc/classes/cse1001/Printf.java
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Keyboard Input
 Starting from Java 5.0
 Java has reasonable facilities for handling keyboard input.

Scanner
class in the java.util package
 A package is a library of classes.
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Using the Scanner Class
 Near the beginning of your program, insert
import java.util.*
 Create an object of the Scanner class
Scanner keyboard =
new Scanner(System.in)
 Read data (an int or a double, for example)
int n1 = keyboard.nextInt();
double d1 = keyboard.nextDouble();
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Some Scanner Class Methods
 Syntax:
Int_Variable =
Object_Name.nextInt();
Double_Variable = Object_Name.nextDouble();
Float_Variable = Object_Name.nextFloat();
String_Variable = Object_Name.next();
String_Variable = Object_Name.nextLine();
Boolean_Variable = Object_Name.nextBoolean();
nextByte(), nextShort(), nextLong()
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Some Scanner Class Methods, cont.
 Examples:
int count = keyboard.nextInt();
double distance = keyboard.nextDouble();
String word = keyboard.next();
String wholeLine = keyboard.nextLine();
 Remember to prompt the user for input:
System.out.print(“Enter an integer: “);
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Keyboard Input Demonstration

class ScannerDemo
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nextLine()Method Caution
 The nextLine() method reads the remainder of the current line, even if it
is empty.
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nextLine()Method Caution, cont.
 Example:
int n;
String s1, s2;
n = keyboard.nextInt();
s1 = keyboard.nextLine();
s2 = keyboard.nextLine();
5440
or bust
n is
set to 5440
but s1 is set to the empty string.
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The Empty String
 String with zero characters
String s3 = “”;

Good for String initialization
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Other Input Delimiters, cont.

class DelimitersDemo
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Documentation and Style: Outline
 Meaningful Names
 Self-Documentation and Comments
 Indentation
 Named Constants

www.cs.fit.edu/~pkc/classes/cse1001/FirstProgramOneLine.java
 Grading
 10% on documentation and comments
 10% on style (variable naming, indentation)
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Documentation and Style
 Most programs are modified over time to respond to new requirements.
 Programs which are easy to read and understand are easy to modify.
 Even if it will be used only once, you have to read it in order to debug it .
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Meaningful Names for Variables
 A variable’s name should suggest its use.
 Observe conventions in choosing names for variables.
 Use only letters and digits.
 Use more than one character.
 “Punctuate” using uppercase letters at word boundaries (e.g. taxRate).
 Start variables with lowercase letters.
 Start class names with uppercase letters.
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Documentation and Comments
 The best programs are self-documenting.
 clean style
 well-chosen names
 Comments are written into a program as needed explain the program.
 They are useful to the programmer, but they are ignored by the compiler.
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When to Use Comments
 Begin each program file with an explanatory comment
 what the program does
 the name of the author
 contact information for the author
 date of the last modification.
 Provide only those comments which the expected reader of the program
file will need in order to understand it.
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Comments Example

class CircleCalculation
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/**
Name: <name>
E-mail address: <email>
Course: cse1001
Section: <?>
Assignment: <HW?>
Date: <date>
Template for CSE 1001
Description: <description>
*/
import java.util.*;
public class <SameClassAndFileNames>
{
public static void main(String[] args)
{
// input from the keyboard
Scanner keyboard = new Scanner(System.in);
}
}
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Comments
 A program can usually be broken into segments/blocks based on the
algorithm, e.g. in HW2:




Prompt the user for input
Input from the keyboard
Calculation
Output to the screen
 Blank line between two segments
 A description (comment) before each segment
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Pseudocode and Comments

Solving a problem
1.
2.
3.

Tip:
1.
2.

Devise an algorithm (steps to solve the problem)
Write the algorithm in pseudocode (semi English, semi Java)
English part of pseudocode becomes comments in your program
type the English part of pesudocode as comments into your program first
write the detailed Java instructions to satisfy/implement the pesudocode
Advantages:
1.
2.
3.
Each line of pseudocode helps you focus on a small task
Pseudocode tells you what steps you want to achieve
No need to add comments later on
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Comments
 A comment can begin with //.
 Everything after these symbols and to the end of the line is treated as a
comment and is ignored by the compiler.
double radius; //in centimeters
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Comments, cont.
 A comment can begin with /* and end with */
 Everything between these symbols is treated as a comment and is ignored
by the compiler.
/* the simplex method is used to
calculate the answer*/
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Comments, cont.
 A javadoc comment, begins with /** and ends with */.
 It can be extracted automatically from Java software.
/** method change requires the number of coins to be nonnegative */
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Indentation
 Indentation should communicate nesting clearly.
 A good choice is four spaces for each level of indentation.
 Indentation should be consistent.
 Indentation should be used for second and subsequent lines of
statements which do not fit on a single line.
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Indentation, cont.
 Indentation does not change the behavior of the program.
 Improper indentation can miscommunicate the behavior of the program.
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Named Constants
 To avoid confusion, always name constants (and variables).
circumference = PI * radius;
is clearer than
circumference = 3.14159 * 6.023;
 Place constants near the beginning of the program.
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Named Constants, cont.
 The value of a constant cannot be changed once it is initialized
public static final double INTEREST_RATE = 6.65;

Consider the interest rate is used many times in the program:
 What if you type 6.65 in some places, but 6.56 in others?
 What if the interested rate has changed to 7.3?
 Is balance * INTEREST_RATE easier to read than
balance * 6.65 ?
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Declaring Constants
 syntax
public static final Type Name = Constant;
 examples
public static final double PI = 3.14159;
public static final String MOTTO = “The customer is always right.”;
 By convention, uppercase letters are used for constants.
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Named Constants

class CircleCalculation2
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Summary
 You have become familiar with Java primitive types (numbers,
characters, etc.).
 You have learned about assignment statements and expressions.
 You have learned about stings.
 You have become familiar with the basics of classes, methods, and
objects.
 You have learned about simple keyboard input and screen output.
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Number Constants
Decimal
0000
0001
0002
0003
0004
0005
0006
0007
0008
0009
0010
0011
0012
0013
0014
0015
0016
0017
0018
0019
0020
0021
0022
0023
0024
0025
0026
0027
0028
0029
0030
0031
0032
Binary
000000
000001
000010
000011
000100
000101
000110
000111
001000
001001
001010
001011
001100
001101
001110
001111
010000
010001
010010
010011
010100
010101
010110
010111
011000
011001
011010
011011
011100
011101
011110
011111
100000
Octal
0000
0001
0002
0003
0004
0005
0006
0007
0010
0011
0012
0013
0014
0015
0016
0017
0020
0021
0022
0023
0024
0025
0026
0027
0030
0031
0032
0033
0034
0035
0036
0037
0040
Hexidecimal
0000
0001
0002
0003
0004
0005
0006
0007
0008
0009
000A
000B
000C
000D
000E
000F
0010
0011
0012
0013
0014
0015
0016
0017
0018
0019
001A
001B
001C
001D
001E
001F
0020
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Binary Representation

Assume an 8-bit type

5 as an integer
 00000101

‘5’ as a character
 00110101 (53 decimal, ASCII)

5.0 as a floating point number
 How?
 What about 5.5?
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Binary Real Numbers
…

23
22
21
20
.
2-1
…
5.5
 101.1

5.25
 101.01

5.125
 101.001

5.75
 101.11
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8 bits only
25

24
23
22
21
20
2-1
2-2
5.5
 101.1 -> 000101 10

5.25
 101.01 -> 000101 01

5.125
 101.001 -> ??

With only 2 places after the point, the precision is .25

What if the point is allowed to move around?
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Floating-point Numbers

Decimal
 54.3
 5.43 x 101

[scientific notation]
Binary
 101.001
 10.1001 x 21
 1.01001 x 22
[more correctly: 10.1001 x 101]
[more correctly: 1.01001 x 1010]
 What can we say about the most significant bit?
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Floating-point Numbers
 General form: sign 1.mantissa x 2exponent
 the most significant digit is right before the dot
 Always 1 [no need to represent it]
 (more details are not discussed here: mantissa has no sign, but sign is
embedded in exponent…)
 1.01001 x 22
 Sign: positive (0)
 Mantissa: 01001
 Exponent: 10 (decimal 2)
 [IEEE standard: “biased exponent”
• exponent + 2numBits-1 - 1
• Example: 2 + 22-1 – 1 = 3 => 11 in binary]
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Java Floating-point Numbers
sign

exponent
mantissa
Sign:
 1 bit [0 is positive]
 Mantissa:
 23 bits in float
 52 bits in double
 Exponent:
 8 bits in float
 11 bits in double
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