2003 Prentice Hall, Inc. All rights reserved. 1 Chapter 2 - Introduction to Java Applications Outline 2.1Introduction 2.2A First Program in Java: Printing

2003 Prentice Hall, Inc. All rights reserved.

1

Chapter 2 - Introduction to Java Applications

Outline2.1 Introduction2.2 A First Program in Java: Printing a Line of Text 2.3 Modifying Our First Java Program 2.4 Displaying Text in a Dialog Box2.5 Another Java Application: Adding Integers2.6 Memory Concepts2.7 Arithmetic2.8 Decision Making: Equality and Relational Operators


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2.1 Introduction

• In this chapter– Introduce examples to illustrate features of Java

– Simple java programs• displaying messages

• geting information from the user

• performing aritmetic and logical opperations

• primitive types in java

• illiustrate decision making


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2.2 A First Program in Java: Printing a Line of Text

• Application– Program that executes using the java interpreter

• Sample program– Show program, then analyze each line

2003 Prentice Hall, Inc.All rights reserved.

Outline4

Welcome1.java

Program Output

1 // Fig. 2.1: Welcome1.java2 // Text-printing program.3 4 public class Welcome1 { 5 6 // main method begins execution of Java application7 public static void main( String args[] )8 {9 System.out.println( "Welcome to Java Programming!" );10 11 } // end method main12 13 } // end class Welcome1

Welcome to Java Programming!


5


– Comments start with: // end of line comment• Comments ignored during program execution

• Document and describe code

• Provides code readability

– Traditional comments: /* ... *//* This is a traditional comment. It can be split over many lines */

– Another line of comments

– Note: line numbers not part of program, added for reference

1 // Fig. 2.1: Welcome1.java

2 // Text-printing program.


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• javadoc comments– delimited by /** end */

– all text between the delimiter is ignored as in treditional comments

– the javadoc utility program• reads javadoc comments and prepare a documentation in

HTML format

• eee Appendix K


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– Blank line• Makes program more readable

• Blank lines, spaces, and tabs are white-space characters

– Ignored by compiler

– Begins class declaration for class Welcome1• Every Java program has at least one user-defined class

• Keyword: words reserved for use by Java

– class keyword followed by class name

• Naming classes: capitalize every word

– SampleClassName

2.2 A Simple Program: Printing a Line of Text

3

4 public class Welcome1 {


8


– Name of class called identifier• Series of characters consisting of letters, digits,

underscores ( _ ) and dollar signs ( $ )

• Does not begin with a digit, has no spaces

• Examples: Welcome1, $value, _value, button7– 7button, first line are invalid

• Java is case sensitive (capitalization matters)

– a1 and A1 are different

– For chapters 2 to 7, use public keyword• Certain details not important now

• Mimic certain features, discussions later



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– Saving files• File name must be class name with .java extension

• Welcome1.java

– Left brace {• Begins body of every class decleration

• Right brace ends declarations (line 13)

– Part of every Java application• Applications begin executing at main

– Parenthesis indicate main is a method (ch. 6)

– Java applications contain one or more methods


7 public static void main( String args[] )


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• Exactly one method must be called main

– Methods can perform tasks and return information• void means main returns no information

• For now, mimic main's first line

– Left brace begins body of method declaration• Ended by right brace } (line 11)

7 public static void main( String args[] )

8 {


11


– Instructs computer to perform an action• Prints string of characters

– String - series characters inside double quotes• White-spaces in strings are not ignored by compiler

– System.out• Standard output object• Print to command window (i.e., MS-DOS prompt)

– Method System.out.println • Displays line of text• Argument inside parenthesis• compleating printing, position the cursor to tbe begiining of

next line

– This line known as a statement• Statements must end with semicolon ;

9 System.out.println( "Welcome to Java Programming!" );


12


– Ends method declaration

– Ends class declaration

– Can add comments to keep track of ending braces

– Lines 8 and 9 could be rewritten as:

– Remember, compiler ignores comments

– Comments can start on same line after code

11 } // end method main

13 } // end class Welcome1


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• Compiling a program– Open a command prompt window, go to directory where

program is stored

– Type javac Welcome1.java– If no errors, Welcome1.class created

• Has bytecodes that represent application

• Bytecodes passed to Java interpreter


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• Executing a program– Type java Welcome1

• Interpreter loads .class file for class Welcome1• .class extension omitted from command

– Interpreter calls method main

Fig. 2.2 Executing Welcome1 in a Microsoft Windows 2000 Command Prompt.


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2.3 Modifying Our First Java Program

• Modify example in Fig. 2.1 to print same contents using different code


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• Displaying single line of text with multiple statemetns– Welcome2.java (Fig. 2.3) produces same output as

Welcome1.java (Fig. 2.1)

– Using different code

– Line 9 displays “Welcome to ” with cursor remaining on printed line

– Line 10 displays “Java Programming! ” on same line with cursor on next line

9 System.out.print( "Welcome to " ); 10 System.out.println( "Java Programming!" );


Outline17

Welcome2.java

1. Comments

2. Blank line

3. Begin class Welcome2

3.1 Method main

4. Method System.out.print

4.1 Method System.out.println

5. end main, Welcome2

Program Output


1 // Fig. 2.3: Welcome2.java2 // Printing a line of text with multiple statements.3 4 public class Welcome2 {5 6 // main method begins execution of Java application7 public static void main( String args[] )8 {9 System.out.print( "Welcome to " ); 10 System.out.println( "Java Programming!" );11 12 } // end method main13 14 } // end class Welcome2

System.out.print keeps the cursor on the same line, so System.out.println continues on the same line.


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• Displaying multiple lines of text with single statement

• Newline characters (\n)– Interpreted as “special characters” by methods System.out.print and System.out.println

– Indicates cursor should be on next line– Welcome3.java (Fig. 2.4)

– Line breaks at \n

• Usage– Can use in System.out.println or System.out.print

to create new lines• System.out.println( "Welcome\nto\nJava\nProgramming!" );

9 System.out.println( "Welcome\nto\nJava\nProgramming!" );


Outline19

Welcome3.java

1. main

2. System.out.println (uses \n for new line)

Program Output

1 // Fig. 2.4: Welcome3.java2 // Printing multiple lines of text with a single statement.3 4 public class Welcome3 {5 6 // main method begins execution of Java application7 public static void main( String args[] )8 {9 System.out.println( "Welcome\nto\nJava\nProgramming!" );10 11 } // end method main12 13 } // end class Welcome3

WelcometoJavaProgramming!

Notice how a new line is output for each \n escape sequence.


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Escape characters– Backslash ( \ )

– Indicates special characters be outputEscape sequence

Description

\n Newline. Position the screen cursor at the beginning of the next line.

\t Horizontal tab. Move the screen cursor to the next tab stop. \r Carriage return. Position the screen cursor at the beginning of

the current line; do not advance to the next line. Any characters output after the carriage return overwrite the characters previously output on that line.

\\ Backslash. Used to print a backslash character. \" Double quote. Used to print a double-quote character. For

example, System.out.println( "\"in quotes\"" ); displays "in quotes"

Fig. 2.5 Some common escape sequences.


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2.4 Displaying Text with printf

• System.out.printf method– displaying formated data in Java SE 5.0

– same output in figure 2çwith printf

System.out.printf(“%s\n%s\n”,

“Welcome to”,”Java programming”);

– Line 9 displays “Welcome to ” with cursor remaining on printed line

– Line 10 displays “Java Programming! ” on same line with cursor on next line

• The method has three arguments– comma seperated list


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2.4 Displaying Text with printf

• Line 9-10 one statement– can be split into more then one line

– ends with ;

– can not be splitted• identifiers or

• strings

• first argumet:– format string

• fixed text

• format specifiers

• format specifiers– begins with a % followed by a character

• s for strings f: float

• d for integers lf:double


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1 // Fig. 2.6: Welcome4.java2 // Printing multiple lines with printf.3 4 public class Welcome4 {5 6 // main method begins execution of Java application7 public static void main( String args[] )8 {9 System.out.printf( “%s\n%s\n “, 10 “Welcome to”,"Java Programming!" );11 12 } // end method main13 14 } // end class Welcome4


output of program


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3.9 Displaying Text in a Dialog Box

• Display– Most Java applications use windows or a dialog box

• We have used command window

– Class JOptionPane allows us to use dialog boxes

• Packages– Set of predefined classes for us to use

– Groups of related classes called packages• Group of all packages known as Java class library or Java

applications programming interface (Java API)

– JOptionPane is in the javax.swing package• Package has classes for using Graphical User Interfaces

(GUIs)


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• Upcoming program– Application that uses dialog boxes

– Explanation will come afterwards

– Demonstrate another way to display output

– Packages, methods and GUI


Outline26

Welcome4.java

1. import declaration

2. Class Welcome4

2.1 main

2.2 showMessageDialog

2.3 System.exit

Program Output

1 // Fig. 2.6: Welcome4.java

2 // Printing multiple lines in a dialog box

3 import javax.swing.JOptionPane; // import class JOptionPane

4


6 public static void main( String args] )

7 {

8 JOptionPane.showMessageDialog(

9 null, "Welcome\nto\nJava\nProgramming!" );

10

11 System.exit( 0 ); // terminate the program

12 }

1 // Fig. 2.6: Welcome4.java2 // Printing multiple lines in a dialog box.3 4 // Java packages 5 import javax.swing.JOptionPane; // program uses JOptionPane6 7 public class Welcome4 {8 9 // main method begins execution of Java application10 public static void main( String args[] )11 {12 JOptionPane.showMessageDialog( 13 null, "Welcome\nto\nJava\nProgramming!" );14 1516 17 } // end method main18 19 } // end class Welcome4


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1 // Fig. 3.17 Dialog1.java2 // Printing multiple lines in a dialog box.3 4 // Java packages 5 import javax.swing.JOptionPane; // program uses JOptionPane6 7 public class Dialog1 {8 9 // main method begins execution of Java application10 public static void main( String args[] )11 {12 JOptionPane.showMessageDialog( 13 null, "Welcome\nto\nJava\nProgramming!" );14 15 } // end method main1617 } // end class Dialog1


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– Lines 1-2: comments as before

– Two groups of packages in Java API– Core packages

• Begin with java• Included with Java 2 Software Development Kit

– Extension packages• Begin with javax• New Java packages

– import declarations • Used by compiler to identify and locate classes used in Java

programs• Tells compiler to load class JOptionPane from javax.swing package

4 // Java packages

5 import javax.swing.JOptionPane; // program uses OptionPane


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– Lines 6-11: Blank line, begin class Welcome4 and main

– Call method showMessageDialog of class JOptionPane

• Requires two arguments

• Multiple arguments separated by commas (,)

• For now, first argument always null• Second argument is string to display

– showMessageDialog is a static method of class JOptionPane• static methods called using class name, dot (.) then

method name

12 JOptionPane.showMessageDialog( 13 null, "Welcome\nto\nJava\nProgramming!" );


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– All statements end with ; • A single statement can span multiple lines

• Cannot split statement in middle of identifier or string

– Executing lines 12 and 13 displays the dialog box

• Automatically includes an OK button

– Hides or dismisses dialog box

• Title bar has string Message


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– Class System part of package java.lang• No import declaration needed

• java.lang automatically imported in every Java program

– Lines 17-19: Braces to end Welcome4 and main


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2.5 Another Java Application: Adding Integers

• Upcoming program– Use input dialogs to input two values from user

– Use message dialog to display sum of the two values


Outline33

Addition.java

1. import

2. class Addition

2.1 Declare variables (name and type)

3. showInputDialog

4. parseInt

5. Add numbers, put result in sum

1 // Fig. 2.9: Addition.java2 // Addition program that displays the sum of two numbers.3 4 // Java packages 5 import javax.swing.JOptionPane; // program uses JOptionPane6 7 public class Addition {8 9 // main method begins execution of Java application10 public static void main( String args[] )11 {12 String firstNumber; // first string entered by user 13 String secondNumber; // second string entered by user14 15 int number1; // first number to add 16 int number2; // second number to add 17 int sum; // sum of number1 and number218 19 // read in first number from user as a String 20 firstNumber = JOptionPane.showInputDialog( "Enter first integer" );21 22 // read in second number from user as a String 23 secondNumber = 24 JOptionPane.showInputDialog( "Enter second integer" );25 26 // convert numbers from type String to type int27 number1 = Integer.parseInt( firstNumber ); 28 number2 = Integer.parseInt( secondNumber ); 29 30 // add numbers 31 sum = number1 + number2;32

Declare variables: name and type.

Input first integer as a String, assign to firstNumber.

Add, place result in sum.

Convert strings to integers.


Outline34

Program output

33 // display result 34 JOptionPane.showMessageDialog( null, "The sum is " + sum,35 "Results", JOptionPane.PLAIN_MESSAGE ); 36 37 38 39 } // end method main40 41 } // end class Addition


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import javax.swing.JOptionPane; // program uses JOptionPane public class Addition { // main method begins execution of Java applicationpublic static void main( String args[] ) { String firstNumber; // first string entered by user String secondNumber; // second string entered by user int number1; // first number to add int number2; // second number to add int sum; // sum of number1 and number2 // read in first number from user as a String firstNumber = JOptionPane.showInputDialog( "Enter first integer" ); // read in second number from user as a String secondNumber = JOptionPane.showInputDialog( "Enter second integer" );


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number1 = Integer.parseInt( firstNumber ); number2 = Integer.parseInt( secondNumber ); // add numbers sum = number1 + number2;// display result JOptionPane.showMessageDialog( null, "The sum is " +

sum, "Results", JOptionPane.PLAIN_MESSAGE );

} // end method main } // end class Addition


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– Location of JOptionPane for use in the program

– Begins public class Addition• Recall that file name must be Addition.java

– Lines 10-11: main

– Declaration• firstNumber and secondNumber are variables

5 import javax.swing.JOptionPane; // program uses JOptionPane

7 public class Addition {

12 String firstNumber; // first string entered by user 13 String secondNumber; // second string entered by user


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– Variables• Location in memory that stores a value

– Declare with name and type before use

• firstNumber and secondNumber are of type String (package java.lang)

– Hold strings

• Variable name: any valid identifier

• Declarations end with semicolons ;

– Can declare multiple variables of the same type at a time

– Use comma separated list

– Can add comments to describe purpose of variables

String firstNumber, secondNumber;

12 String firstNumber; // first string entered by user 13 String secondNumber; // second string entered by user


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– Declares variables number1, number2, and sum of type int• int holds integer values (whole numbers): i.e., 0, -4, 97• Types float and double can hold decimal numbers

• Type char can hold a single character: i.e., x, $, \n, 7

• Primitive types - more in Chapter 4

15 int number1; // first number to add 16 int number2; // second number to add 17 int sum; // sum of number1 and number2


40


– Reads String from the user, representing the first number to be added

• Method JOptionPane.showInputDialog displays the following:

• Message called a prompt - directs user to perform an action

• Argument appears as prompt text

• If wrong type of data entered (non-integer) or click Cancel, error occurs

20 firstNumber = JOptionPane.showInputDialog( "Enter first integer" );


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– Result of call to showInputDialog given to firstNumber using assignment operator =

• Assignment statement

• = binary operator - takes two operands

– Expression on right evaluated and assigned to variable on left

• Read as: firstNumber gets value of JOptionPane.showInputDialog( "Enter first integer" )

20 firstNumber = JOptionPane.showInputDialog( "Enter first integer" );


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– Similar to previous statement• Assigns variable secondNumber to second integer input

– Method Integer.parseInt• Converts String argument into an integer (type int)

– Class Integer in java.lang• Integer returned by Integer.parseInt is assigned to

variable number1 (line 27)

– Remember that number1 was declared as type int• Line 28 similar

23 secondNumber = 24 JOptionPane.showInputDialog( "Enter second integer" );

27 number1 = Integer.parseInt( firstNumber ); 28 number2 = Integer.parseInt( secondNumber );


43


– Assignment statement• Calculates sum of number1 and number2 (right hand side)

• Uses assignment operator = to assign result to variable sum• Read as: sum gets the value of number1 + number2• number1 and number2 are operands

31 sum = number1 + number2;


44


– Use showMessageDialog to display results

– "The sum is " + sum• Uses the operator + to "add" the string literal "The sum is"

and sum• Concatenation of a String and another type

– Results in a new string

• If sum contains 117, then "The sum is " + sum results in the new string "The sum is 117"

• Note the space in "The sum is "

34 JOptionPane.showMessageDialog( null, "The sum is " + sum,35 "Results", JOptionPane.PLAIN_MESSAGE );


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– Different version of showMessageDialog• Requires four arguments (instead of two as before)

• First argument: null for now

• Second: string to display

• Third: string in title bar

• Fourth: type of message dialog with icon

– Line 35 no icon: JOptionPane.PLAIN_MESSAGE

34 JOptionPane.showMessageDialog( null, "The sum is " + sum,35 "Results", JOptionPane.PLAIN_MESSAGE );


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Message dialog type Icon Description

JOptionPane.ERROR_MESSAGE

Displays a dialog that indicates an error to the user.

JOptionPane.INFORMATION_MESSAGE

Displays a dialog with an informational message to the user. The user can simply dismiss the dialog.

JOptionPane.WARNING_MESSAGE

Displays a dialog that warns the user of a potential problem.

JOptionPane.QUESTION_MESSAGE

Displays a dialog that poses a question to the user. This dialog normally requires a response, such as clicking on a Yes or a No button.

JOptionPane.PLAIN_MESSAGE no icon Displays a dialog that simply contains a

message, with no icon. Fig. 2.12 JOptionPane constants for message dialogs.


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• Upcoming program– Use Scanner class to input two values from the console


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1 // Fig. 2.7: Addition.java2 // Addition program that displays the sum of two

numbers. 3 import java.util.Scanner; // program uses class Scanner4 5 public class Addition 6 {7 // main method begins execution of Java application8 public static void main( String args[] )9 {10 // criate Scanner to optain input ftom comment window11 Scanner input = new Scanner(System.in);12 13 int number1; // first number to add 14 int number2; // second number to add 15 int sum; // sum of two numbers1617 System.out.print(“Enter first integer:”);18 number1 = input.nextInt(); //read first number


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1920 System.out.print(“Enter second integer:”);21 number2 = input.nextInt(); //read first number 2223 sum = number1 + number224 25 System.out.pritf(“Sum is %d\n”, sum);26 27 } // end of main 28 } // end of calss Addition

The programs output:

Enter first integer 45Enter second integer 72Sum is 117


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inport java.util.Scanner;• line 3 inport decleration

– help the compiler to locate a class used in this program

– program uses predefined Scanner class in the java.util package

• if the inport decleration is not used– Scanner class should be used like that

• java.util.Scanner

– Example:• Scanner input = new Scanner(System.in);

– Should be replaced with• java.util.Scanner input = new java.util.Scanner(System.in);


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Scanner input = new Scanner(System.in);• line 11 variable decleration statement

– variable name input– varaible type Scanner

• Names are identifiers• Scanner

– enables to read data (numbers, strings)– sources:

• file on a disk• user from keyboard

• before using a Scanner type variable– criate it and– specify the source of data


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• in line 11 Scanner variable input should be initialized

• the expression– new Scanner(System.in)

– criates a Scanner objcet that reads data typed by the user from the keyboard

• System.out: standard output objcet– display characters in the command window

• Syste.in: standard input objcet– enables users to enter input from keyboard


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number1 = input.nextInt();• line 18 Scanner object input’s nextInt method

– to obtain an integer from the user at the keyboard

– if the user types an non ingeger value at the keyboard• the program terminates – logic runtime error

– nextInt method return an intger variable – input by the user

– by the assignment opperator • assigned to int variable number1


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• Note that– nextInt method is called with the input object a Scanner type

objcet - general format

– objcet name.method name

• In the previous example– JOptionPane’s showInputDialog method is called with the

class name – in general

– class name.method name

– thess are static method which are used by class names

– non-static mehods are used with objcets criated from classes


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2.6 Memory Concepts

• Variables – Every variable has a name, a type, a size and a value

• Name corresponds to location in memory

– When new value is placed into a variable, replaces (and destroys) previous value

– Reading variables from memory does not change them


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2.6 Memory Concepts

• Visual Representation– Sum = 0; number1 = 1; number2 = 2;

– Sum = number1 + number2; after execution of statement

sum 0

sum 3


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2.7 Arithmetic

• Arithmetic calculations used in most programs– Usage

• * for multiplication

• / for division

• +, -• No operator for exponentiation (more in Chapter 5)

– Integer division truncates remainder7 / 5 evaluates to 1

– Remainder operator % returns the remainder 7 % 5 evaluates to 2


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Casting

• int i=5,j=2;

• What is i / j

• : 5 / 2 = 2 integer division– Both nominator and denominator are integers

• İf you want to get a decimal number

• Use casting

• (float) i / j = 5.0 / 2 = 2.5

• (double) i / j = 5.0 / 2 =2.5 or

• i / (double)j = 5/ 2.0 =2.5

• The original values of i or j does not change they temporarily promoted to a (double float) in evaluationg the expression


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2.7 Arithmetic

Operator(s) Operation(s) Order of evaluation (precedence) * /

%

Multiplication Division Remainder

Evaluated first. If there are several of this type of operator, they are evaluated from left to right.

+ -

Addition Subtraction

Evaluated next. If there are several of this type of operator, they are evaluated from left to right.

Fig. 2.12 Precedence of arithmetic operators.


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4.11 Compound Assignment Operators

• Assignment Operators– Abbreviate assignment expressions

– Any statement of form• variable = variable operator expression;

– Can be written as• variable operator= expression;

– e.g., addition assignment operator +=• c = c + 3

– can be written as• c += 3


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Assignment operator

Sample expression

Explanation Assigns

Assume: int c = 3, d = 5, e = 4, f = 6, g = 12;

+= c += 7 c = c + 7 10 to c -= d -= 4 d = d - 4 1 to d *= e *= 5 e = e * 5 20 to e /= f /= 3 f = f / 3 2 to f %= g %= 9 g = g % 9 3 to g Fig. 4.12 Arithmetic assignment operators.


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4.12 Increment and Decrement Operators

• Unary increment operator (++)– Increment variable’s value by 1

• Unary decrement operator (--)– Decrement variable’s value by 1

• Preincrement / predecrement operator• Post-increment / post-decrement operator


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Operator Called Sample expression

Explanation

++ preincrement ++a Increment a by 1, then use the new value of a in the expression in which a resides.

++ postincrement a++ Use the current value of a in the expression in which a resides, then increment a by 1.

-- predecrement --b Decrement b by 1, then use the new value of b in the expression in which b resides.

-- postdecrement b-- Use the current value of b in the expression in which b resides, then decrement b by 1.

Fig. 4.13 The increment and decrement operators.


Outline64

Increment.java

Line 13 postincrement

Line 21 preincrement

1 // Fig. 4.14: Increment.java2 // Preincrementing and postincrementing operators.3 4 public class Increment {5 6 public static void main( String args[] )7 {8 int c;9 10 // demonstrate postincrement11 c = 5; // assign 5 to c12 System.out.println( c ); // print 513 System.out.println( c++ ); // print 5 then postincrement14 System.out.println( c ); // print 6 15 16 System.out.println(); // skip a line17 18 // demonstrate preincrement19 c = 5; // assign 5 to c20 System.out.println( c ); // print 521 System.out.println( ++c ); // preincrement then print 622 System.out.println( c ); // print 6 23 24 } // end main25 26 } // end class Increment

556

566

Line 13 postincrements c

Line 21 preincrements c


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Operators Associativity Type ++ -- right to left unary postfix

++ -- + - (type) right to left unary * / % left to right multiplicative + - left to right additive < <= > >= left to right relational == != left to right equality ?: right to left conditional = += -= *= /= %= right to left assignment Fig. 4.15 Precedence and associativity of the operators discussed so far.


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4.13 Primitive Types

• Primitive types– “building blocks” for more complicated types

• Java is strongly typed– All variables in a Java program must have a type

• Java primitive types– portable across computer platforms that support Java


67

Type Size in bits Values Standard boolean true or false

[Note: The representation of a boolean is specific to the Java Virtual Machine on each computer platform.]

char 16 '\u0000' to '\uFFFF' (0 to 65535)

(ISO Unicode character set)

byte 8 –128 to +127 (–27 to 27 – 1)

short 16 –32,768 to +32,767 (–215 to 215 – 1)

int 32 –2,147,483,648 to +2,147,483,647 (–231 to 231 – 1)

long 64 –9,223,372,036,854,775,808 to +9,223,372,036,854,775,807 (–263 to 263 – 1)

float 32 Negative range: –3.4028234663852886E+38 to –1.40129846432481707e–45 Positive range: 1.40129846432481707e–45 to 3.4028234663852886E+38

(IEEE 754 floating point)

double 64 Negative range: –1.7976931348623157E+308 to –4.94065645841246544e–324 Positive range: 4.94065645841246544e–324 to 1.7976931348623157E+308

(IEEE 754 floating point)

Fig. 4.16 The J ava primitive types.


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Boolean Variables

• A primitive variable in java– either true or false

• Decleration– boolean b1,b2; // declaring two boolean variables

– boolean b3= true;// declaring and initilizing

– b1 = 2<1;

– /* 2<1 is a logical expression whose value is false

• right side of expression is false• it is assigned to b1• so b1 is false */


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• b2 = b1 && b3;• /* b1 is false b3 is true • so b2 is false */• System.out.println(“b1 is ”+b1);• System.out.println(“b2 && b3 is ”+(b2 && b3));• System.out.printf(“b2 && b3 is %b\n”, • (b2 && b3));• if(b1)• System.out.println(“b1 is true”);• else• System.out.println(“b1 is false”);


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• The output is:

b1 is false

b2 && b3 is false

b2 && b3 is false

b1 is false


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2.8 Decision Making: Equality and Relational Operators

• if control statement– Simple version in this section, more detail later

– If a condition is true, then the body of the if statement executed

– Control always resumes after the if structure

– Conditions for if statements can be formed using equality or relational operators (next slide)

if ( condition ) statement executed if condition

true• No semicolon needed after condition

– Else conditional task not performed


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• condition should be a logical expression not an aritmetic expression as in C

• Example:– int i =1; if(i-1)

System.out.printf(“true”);else System.out.printf(“false”);Syntax error in java as

– int i =1;– boolean b = i-1==0; if(b) // or if(i-1==0)

System.out.printf(“true”);else System.out.printf(“false”);


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• Upcoming program uses if statements– Discussion afterwards

Standard algebraic equality or relational operator

J ava equality or relational operator

Example of J ava condition

Meaning of J ava condition

Equality operators = == x == y x is equal to y != x != y x is not equal to y Relational operators > > x > y x is greater than y < < x < y x is less than y >= x >= y x is greater than or equal to y <= x <= y x is less than or equal to y Fig. 2.19 Equality and relational operators.


Outline74

Comparison.java

1. import

2. Class Comparison

2.1 main

2.2 Declarations

2.3 Input data (showInputDialog)

2.4 parseInt

2.5 Initialize result

1 // Fig. 2.20: Comparison.java2 // Compare integers using if statements, relational operators 3 // and equality operators.4 5 // Java packages6 import javax.swing.JOptionPane;7 8 public class Comparison {9 10 // main method begins execution of Java application11 public static void main( String args[] )12 {13 String firstNumber; // first string entered by user14 String secondNumber; // second string entered by user15 String result; // a string containing the output16 17 int number1; // first number to compare18 int number2; // second number to compare19 20 // read first number from user as a string21 firstNumber = JOptionPane.showInputDialog( "Enter first integer:" );22 23 // read second number from user as a string24 secondNumber =25 JOptionPane.showInputDialog( "Enter second integer:" );26 27 // convert numbers from type String to type int28 number1 = Integer.parseInt( firstNumber );29 number2 = Integer.parseInt( secondNumber );30 31 // initialize result to empty String32 result = ""; 33


Outline75

Comparison.java

3. if statements

4. showMessageDialog

34 if ( number1 == number2 ) 35 result = result + number1 + " == " + number2;36 37 if ( number1 != number2 ) 38 result = result + number1 + " != " + number2;39 40 if ( number1 < number2 ) 41 result = result + "\n" + number1 + " < " + number2;42 43 if ( number1 > number2 ) 44 result = result + "\n" + number1 + " > " + number2;45 46 if ( number1 <= number2 ) 47 result = result + "\n" + number1 + " <= " + number2;48 49 if ( number1 >= number2 ) 50 result = result + "\n" + number1 + " >= " + number2;51 52 // Display results 53 JOptionPane.showMessageDialog( null, result, "Comparison Results",54 JOptionPane.INFORMATION_MESSAGE ); 55 5657 58 } // end method main59 60 } // end class Comparison

Test for equality, create new string, assign to result.

Notice use of JOptionPane.INFORMATION_MESSAGE


Outline76

Program Output


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1 // Fig. 2.20: Comparison.java2 // Compare integers using if statements, relational operators 3 // and equality operators.4 5 // Java packages6 import javax.swing.JOptionPane;7 8 public class Comparison {9 10 // main method begins execution of Java application11 public static void main( String args[] )12 {13 String firstNumber; // first string entered by user14 String secondNumber; // second string entered by user15 String result; // a string containing the output16 17 int number1; // first number to compare18 int number2; // second number to compare


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20 // read first number from user as a string21 firstNumber = JOptionPane.showInputDialog( "Enter first integer:" );22 23 // read second number from user as a string24 secondNumber =25 JOptionPane.showInputDialog( "Enter second integer:" );26 27 // convert numbers from type String to type int28 number1 = Integer.parseInt( firstNumber );29 number2 = Integer.parseInt( secondNumber );30 31 // initialize result to empty String32 result = "";


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34 if ( number1 == number2 ) 35 result = result + number1 + " == " + number2;36 37 if ( number1 != number2 ) 38 result = result + number1 + " != " + number2;39 40 if ( number1 < number2 ) 41 result = result + "\n" + number1 + " < " + number2;42 43 if ( number1 > number2 ) 44 result = result + "\n" + number1 + " > " + number2;45 46 if ( number1 <= number2 ) 47 result = result + "\n" + number1 + " <= " + number2;48 49 if ( number1 >= number2 ) 50 result = result + "\n" + number1 + " >= " + number2;


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52 // Display results

53 JOptionPane.showMessageDialog( null, result, "Comparison Results",

54 JOptionPane.INFORMATION_MESSAGE );

55

56

57

58 } // end method main

59

60 } // end class Comparison


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– Lines 1-12: Comments, import JOptionPane, begin class Comparison and main

– Lines 13-18: declare variables• Can use comma-separated lists instead:

– Lines 21-30: obtain user-input numbers and parses input string into integer variables

13 String firstNumber, 14 secondNumber, 15 result;


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– Initialize result with empty string

– if statement to test for equality using (==)• If variables equal (condition true)

– result concatenated using + operator

– result = result + other strings– Right side evaluated first, new string assigned to result

• If variables not equal, statement skipped

32 result = "";

34 if ( number1 == number2 ) 35 result = result + number1 + " == " + number2;


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– Lines 37-50: other if statements testing for less than, more than, etc.

• If number1 = 123 and number2 = 123

– Line 34 evaluates true (if number1 = = number 2)

• Because number1 equals number2

– Line 40 evaluates false (if number1 < number 2)

• Because number1 is not less than number2

– Line 49 evaluates true (if number1 >= number2)

• Because number1 is greater than or equal to number2

– Lines 53-54: result displayed in a dialog box using showMessageDialog


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• Precedence of operators– All operators except for = (assignment) associates from left

to right• For example: x = y = z is evaluated x = (y = z)

Operators Associativity Type * / % left to right multiplicative + - left to right additive < <= > >= left to right relational == != left to right equality = right to left assignment Fig. 2.21 Precedence and associativity of the operators discussed so far.


85

4.5 if Single-Selection Statement

• Single-entry/single-exit control structure• Perform action only when condition is true• Action/decision programming model


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Fig 4.3 if single-selections statement activity diagram.

[grade >= 60]

[grade < 60]

print “Passed”


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4.6 if…else Selection Statement

• Perform action only when condition is true• Perform different specified action when condition

is false• Conditional operator (?:)• Nested if…else selection structures


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Fig 4.4 if…else double-selections statement activity diagram.

[grade >= 60][grade < 60]print “Failed” print “Passed”


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5.8 Logical Operators

• Logical operators– Allows for forming more complex conditions

– Combines simple conditions

• Java logical operators– && (conditional AND)

– & (boolean logical AND)

– || (conditional OR)

– | (boolean logical inclusive OR)

– ^ (boolean logical exclusive OR)

– ! (logical NOT)


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expression1 expression2 expression1 && expression2

false false false false true false true false false true true true Fig. 5.15 && (conditional AND) operator truth table.

expression1 expression2 expression1 || expression2

false false false false true true true false true true true true Fig. 5.16 || (conditional OR) operator truth table.


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expression1 expression2 expression1 ^ expression2

false false false false true true true false true true true false Fig. 5.17 ^ (boolean logical exclusive OR) operator truth table.

expression !expression false true true false Fig. 5.18 ! (logical negation, or logical NOT) operator truth table.


Outline92

LogicalOperators.java

Lines 16-20

Lines 23-27

1 // Fig. 5.19: LogicalOperators.java2 // Logical operators.3 import javax.swing.*;4 5 public class LogicalOperators 6 7 public static void main( String args[] )8 {9 // create JTextArea to display results10 JTextArea outputArea = new JTextArea( 17, 20 );11 12 // attach JTextArea to a JScrollPane so user can scroll results13 JScrollPane scroller = new JScrollPane( outputArea );14 15 // create truth table for && (conditional AND) operator16 String output = "Logical AND (&&)" + 17 "\nfalse && false: " + ( false && false ) +18 "\nfalse && true: " + ( false && true ) +19 "\ntrue && false: " + ( true && false ) +20 "\ntrue && true: " + ( true && true );21 22 // create truth table for || (conditional OR) operator23 output += "\n\nLogical OR (||)" +24 "\nfalse || false: " + ( false || false ) +25 "\nfalse || true: " + ( false || true ) +26 "\ntrue || false: " + ( true || false ) +27 "\ntrue || true: " + ( true || true );28

Conditional AND truth table

Conditional OR truth table


Outline93


Lines 30-34

Lines 37-41

Lines 44-48

Lines 51-53

29 // create truth table for & (boolean logical AND) operator30 output += "\n\nBoolean logical AND (&)" +31 "\nfalse & false: " + ( false & false ) +32 "\nfalse & true: " + ( false & true ) +33 "\ntrue & false: " + ( true & false ) +34 "\ntrue & true: " + ( true & true );35 36 // create truth table for | (boolean logical inclusive OR) operator37 output += "\n\nBoolean logical inclusive OR (|)" +38 "\nfalse | false: " + ( false | false ) +39 "\nfalse | true: " + ( false | true ) +40 "\ntrue | false: " + ( true | false ) +41 "\ntrue | true: " + ( true | true );42 43 // create truth table for ^ (boolean logical exclusive OR) operator44 output += "\n\nBoolean logical exclusive OR (^)" +45 "\nfalse ^ false: " + ( false ^ false ) +46 "\nfalse ^ true: " + ( false ^ true ) +47 "\ntrue ^ false: " + ( true ^ false ) +48 "\ntrue ^ true: " + ( true ^ true );49 50 // create truth table for ! (logical negation) operator51 output += "\n\nLogical NOT (!)" +52 "\n!false: " + ( !false ) + 53 "\n!true: " + ( !true );54 55 outputArea.setText( output ); // place results in JTextArea56

Logical NOT truth table

Boolean logical exclusive OR truth table

Boolean logical inclusive OR truth table

Boolean logical AND truth table


Outline94


57 JOptionPane.showMessageDialog( null, scroller,58 "Truth Tables", JOptionPane.INFORMATION_MESSAGE );59 60 System.exit( 0 ); // terminate application61 62 } // end main63 64 } // end class LogicalOperators


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Operators Associativity Type ++ -- right to left unary postfix ++ -- + - ! (type)

right to left unary

* / % left to right multiplicative + - left to right additive < <= > >= left to right relational == != left to right equality & left to right boolean logical AND ^ left to right boolean logical exclusive OR | left to right boolean logical inclusive OR && left to right conditional AND || left to right conditional OR ?: right to left conditional = += -= *= /= %= right to left assignment Fig. 5.20 Precedence/associativity of the operators discussed so far.


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What is the output

int i =1;boolean b1 = ++i == i++;boolean b2 = i++ == ++i;System.out.printf(“%d%b%b”,i,b1,b2);----------------String s1 = 1 + 2 + “what is this”;String s2 = “what is this” + 1 + 2;System.out.printf(“%s\n%s”,s1,s2);----------------------String s3 = “”+1 + 2 + “what is this”;String s4 = “what is this” + (1 + 2);System.out.printf(“%s\n%s”,s3,s4);


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What is the output

----------------int i =1;System.out.printf(“%d %d %d”,++i,i,i++);System.out.printf(“%d %d %d”, i++,i,++i);

----------------------int i =1;System.out.printf(“%d %d %d”,++i,i,i++);System.out.printf(“%d %d %d”, i++,i,++i);


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Exercise

• A user intends to withdraw money from a ATM machine by entering the amount she needs

• The ATM machine contains a set of notes e.g.:– 100 TL, 50 TL, 20 TL...– For the time beeing assume that there is no availability problem

for any of these notes– ATM first pays 100 TLs as much as possible then pays 50 TLs and

so on

• e.g.: the user demands 328– Available notes are 100,50,20,10– ATM pays 3 100s , 1 20 but the 8 TL can not be paid

• e.g.: the user demands 483– Available notes are 100,50,20,10– ATM pays 4 100s , 1 50 , 1 20, 1 10 but the 3 TL can not be paid


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• Write a program obtaining the amout of money from the user and outputing how it is paid with availabe note in the ATM. The program should also give the amout of money that can not be paid.

• Externsion:• You can extend the problem to TL and kurushes

with say 2 digits• Availabel notes are say 100,50,20,10,5,1• Available coints are 50,25,10,5


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• e.g.: how to pay 37.86 TL • 1: 20 + 1: 10 + 1: 5 + 2: 1 notes• 1: 50 + 1: 25 + 1: 10 coins• 1 krush can not be paid


101

Exercise

• Leap year problem• Given a year determine whether it is a leap year or

not• i. A year is a leap year if it is divided by four

– 2004, 2000, 1900 are but– 2005, 2001 not

• ii. in addition it can not be divided by 100– 2004 is but– 2000 is not as 2000 mode 100 = 0

• iii. in addition it is divided by 400– 2000 is as 2000 mde 400 = 0 but– 1900 is not, as 1900 mode 100 =0 by B and 1900 mode 400

=300 not zero


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A. Year mode 4 = 0

B year mode 100 = 0

C year mode 400=0

2000

2004

1900


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• i can be codes as• İf (year % 4 == 0)• System.out.print(year +“ is a leap year”);

• ii can be coded as• if (year % 4 == 0 && year % 100 !=0 )• System.out.print(year +“ is a leap year”);

• Solve iii yourself• Solve the same problem both i ii and iii without

using logical oppertators (and or not)


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• For case ii

• year b1 b2 b1&&b2

year % 4 ==0 year % 100 !=0

----------------------------------------------------------

2008 true true true

2000 true false false


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• We are going to use this in our coming examples– To calculste difference between days

– How many days you live?

– To calculate punishments as a function of number of days between due date and today


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Exercise

• Progressive taxation • Given the yearly income of a person the amout of

income tax is progressively increases. Say– For the first 10,000 TL - no income

– Between 10,000 and 20,000 – 5%

– Between 20,000 and 50,000 - 10%

– After 50,000 – 20%

• E.g.: if income is 15,000– Tax = 0.05*(15,000-10,000) = 250

• E.g.: if income is 35,000– Tax = 0.05*(20,000-10,000) + 0.1*(35,000-20,000)=2000


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• Write program taking yearly income and calculating and printing the income tax due of a person – For the time being the tax rates and slices are fixed and

assigned in the program

• i – using the if else structure• ii – using only simple if sturcture without using

else part

Documents

2003 Prentice Hall, Inc. All rights reserved. 1 Chapter 2 - Introduction to Java Applications Outline 2.1Introduction 2.2A First Program in Java: Printing