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1
Chapter 2 - Introduction to Java
Applications
Outline
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
Introduction
A First Program in Java: Printing a Line of Text
Modifying Our First Java Program
Displaying Text in a Dialog Box
Another Java Application: Adding Integers
Memory Concepts
Arithmetic
Decision Making: Equality and Relational Operators
2003 Prentice Hall, Inc. All rights reserved.
2
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
2003 Prentice Hall, Inc. All rights reserved.
3
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.
4
Outline
1
2
3
4
5
6
7
8
9
10
11
12
13
// Fig. 2.1: Welcome1.java
// Text-printing program.
Welcome1.java
public class Welcome1 {
// main method begins execution of Java application
public static void main( String args[] )
{
System.out.println( "Welcome to Java Programming!" );
} // end method main
} // end class Welcome1
Welcome to Java Programming!
Program Output
2003 Prentice Hall, Inc.
All rights reserved.
5
2.2
1
A First Program in Java: Printing a
Line of Text
// Fig. 2.1: Welcome1.java
– 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 */
2
// Text-printing program.
– Another line of comments
– Note: line numbers not part of program, added for reference
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6
2.2
A First Program in Java: Printing a
Line of Text
• 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
2003 Prentice Hall, Inc. All rights reserved.
7
2.2
A Simple Program: Printing a Line of
Text
3
– Blank line
• Makes program more readable
• Blank lines, spaces, and tabs are white-space characters
– Ignored by compiler
4
public class Welcome1 {
– 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
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8
2.2
4
A Simple Program: Printing a Line of
Text
public class Welcome1 {
– 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
2003 Prentice Hall, Inc. All rights reserved.
9
2.2
4
A Simple Program: Printing a Line of
Text
public class Welcome1 {
– 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)
7
public static void main( String args[] )
– 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
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10
2.2
7
A Simple Program: Printing a Line of
Text
public static void main( String args[] )
• 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
8
{
– Left brace begins body of method declaration
• Ended by right brace } (line 11)
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11
2.2
9
A Simple Program: Printing a Line of
Text
System.out.println( "Welcome to Java Programming!" );
– 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 ;
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12
2.2
11
A Simple Program: Printing a Line of
Text
} // end method main
– Ends method declaration
13
–
–
–
–
–
} // end class Welcome1
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
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13
2.2
A Simple Program: Printing a Line of
Text
• 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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14
2.2
A Simple Program: Printing a Line of
Text
• 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.
2003 Prentice Hall, Inc. All rights reserved.
15
2.3
Modifying Our First Java Program
• Modify example in Fig. 2.1 to print same contents
using different code
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16
2.3
Modifying Our First Java Program
• 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
9
10
System.out.print( "Welcome to " );
System.out.println( "Java Programming!" );
– Line 9 displays “Welcome to ” with cursor remaining on
printed line
– Line 10 displays “Java Programming! ” on same line with
cursor on next line
2003 Prentice Hall, Inc. All rights reserved.
17
Outline
Welcome2.java
1. Comments
1
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4
5
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10
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13
14
// Fig. 2.3: Welcome2.java
// Printing a line of text with multiple statements.
public class Welcome2 {
// main method begins execution of Java application
public static void main( String args[] )
{
System.out.print( "Welcome to " );
System.out.println( "Java Programming!" );
} // end method main
} // end class Welcome2
System.out.print keeps the cursor on
the same line, so System.out.println
continues on the same line.
Welcome to Java Programming!
2. Blank line
3. Begin class
Welcome2
3.1 Method main
4. Method
System.out.prin
t
4.1 Method
System.out.prin
tln
5. end main,
Welcome2
Program
Output
2003 Prentice Hall, Inc.
All rights reserved.
18
2.3
Modifying Our First Java Program
• 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)
9
System.out.println( "Welcome\nto\nJava\nProgramming!" );
– 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!" );
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19
Outline
1
2
3
4
5
6
7
8
9
10
11
12
13
// Fig. 2.4: Welcome3.java
// Printing multiple lines of text with a single statement.
Welcome3.java
public class Welcome3 {
1. main
// main method begins execution of Java application
public static void main( String args[] )
{
System.out.println( "Welcome\nto\nJava\nProgramming!" );
} // end method main
2.
System.out.prin
tln (uses \n for new
line)
} // end class Welcome3
Program Output
Welcome
to
Java
Programming!
Notice how a new line is output for each \n
escape sequence.
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20
2.3
Modifying Our First Java Program
Escape characters
– Backslash ( \ )
– Indicates special characters be output
Esc a p e
De sc rip tio n
se q ue nc e
\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 So m e c o m m o n e sc a p e se q ue nc e s.
2003 Prentice Hall, Inc. All rights reserved.
21
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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22
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
• d for integers
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f: float
lf:double
23
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// Fig. 2.6: Welcome4.java
// Printing multiple lines with printf.
public class Welcome4 {
// main method begins execution of Java application
public static void main( String args[] )
{
System.out.printf( “%s\n%s\n “,
“Welcome to”,"Java Programming!" );
} // end method main
} // end class Welcome4
output of program
Welcome to
Java Programming!
2003 Prentice Hall, Inc. All rights reserved.
24
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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25
3.9
Displaying Text in a Dialog Box
• Upcoming program
–
–
–
–
Application that uses dialog boxes
Explanation will come afterwards
Demonstrate another way to display output
Packages, methods and GUI
2003 Prentice Hall, Inc. All rights reserved.
26
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1// //
Fig.
2.6:
Welcome4.java
Fig.
2.6:
Welcome4.java
// Printing multiple lines in a dialog box.
2 // Printing multiple lines in a dialog box
3// import
javax.swing.JOptionPane; // import class JOptionPane
Java packages
4import javax.swing.JOptionPane; // program uses JOptionPane
5 public class Welcome4 {
public class Welcome4 {
6
public static void main( String args] )
// main method begins execution of Java application
7
{
public static void main( String args[] )
8 {
JOptionPane.showMessageDialog(
JOptionPane.showMessageDialog(
9
null, "Welcome\nto\nJava\nProgramming!" );
null, "Welcome\nto\nJava\nProgramming!" );
10
11
12
System.exit( 0 );
}
} // end method main
} // end class Welcome4
// terminate the program
Outline
Welcome4.java
1. import
declaration
2. Class Welcome4
2.1 main
2.2
showMessageDial
og
2.3 System.exit
Program Output
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27
1
// Fig. 3.17 Dialog1.java
2
// Printing multiple lines in a dialog box.
3
4
// Java packages
5
import javax.swing.JOptionPane; // program uses
JOptionPane
6
7
public class Dialog1 {
8
9
// main method begins execution of Java application
10
public static void main( String args[] )
11
{
12
JOptionPane.showMessageDialog(
13
null, "Welcome\nto\nJava\nProgramming!" );
14
15
} // end method main
16
17 } // end class Dialog1
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28
3.9
Displaying Text in a Dialog Box
– Lines 1-2: comments as before
4
// Java packages
– 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
5
import javax.swing.JOptionPane;
// program uses OptionPane
– import declarations
• Used by compiler to identify and locate classes used in Java
programs
• Tells compiler to load class JOptionPane from
javax.swing package
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29
3.9
Displaying Text in a Dialog Box
– Lines 6-11: Blank line, begin class Welcome4 and main
12
13
JOptionPane.showMessageDialog(
null, "Welcome\nto\nJava\nProgramming!" );
– 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
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30
3.9
Displaying Text in a Dialog Box
– 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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31
3.9
Displaying Text in a Dialog Box
– 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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32
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
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1
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// Fig. 2.9: Addition.java
// Addition program that displays the sum of two numbers.
// Java packages
import javax.swing.JOptionPane;
Outline
Addition.java
// program uses JOptionPane
1. import
public class Addition {
name and
// main method begins executionDeclare
of Javavariables:
application
public static void main( String args[] )
{
String firstNumber;
// first string entered by user
String secondNumber; // second string entered by user
int number1;
int number2;
int sum;
type.
// first number to add
Input
first integer
// second
number
to add as a String,
// sum to
offirstNumber.
number1 and number2
2.1 Declare variables
(name and type)
assign
// 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" );
2. class Addition
3.
showInputDialog
4. parseInt
5. Add numbers, put
result in sum
Convert strings to integers.
// convert numbers from type StringAdd,
to type
placeint
result
number1 = Integer.parseInt( firstNumber );
number2 = Integer.parseInt( secondNumber );
// add numbers
sum = number1 + number2;
in sum.
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34
33
34
35
36
37
38
39
40
41
// display result
JOptionPane.showMessageDialog( null, "The sum is " + sum,
"Results", JOptionPane.PLAIN_MESSAGE );
Outline
} // end method main
} // end class Addition
Program output
2003 Prentice Hall, Inc.
All rights reserved.
35
import javax.swing.JOptionPane; // program uses JOptionPane
public class Addition {
// main method begins execution of Java application
public static void main( String args[] )
{
String firstNumber; // first string entered by user
String secondNumber; // second string entered by user
int number1;
int number2;
int sum;
// first number to add
// second number to add
// 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" );
2003 Prentice Hall, Inc. All rights reserved.
36
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
2003 Prentice Hall, Inc. All rights reserved.
37
2.5
5
Another Java Application: Adding
Integers
import javax.swing.JOptionPane;
// program uses JOptionPane
– Location of JOptionPane for use in the program
7
public class Addition {
– Begins public class Addition
• Recall that file name must be Addition.java
– Lines 10-11: main
12
13
String firstNumber;
String secondNumber;
// first string entered by user
// second string entered by user
– Declaration
• firstNumber and secondNumber are variables
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38
2.5
12
13
Another Java Application: Adding
Integers
String firstNumber;
String secondNumber;
// first string entered by user
// second string entered by user
– 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 ;
String firstNumber, secondNumber;
– Can declare multiple variables of the same type at a time
– Use comma separated list
– Can add comments to describe purpose of variables
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39
2.5
15
16
17
Another Java Application: Adding
Integers
int number1;
int number2;
int sum;
// first number to add
// second number to add
// sum of number1 and number2
– 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
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40
2.5
20
Another Java Application: Adding
Integers
firstNumber = JOptionPane.showInputDialog( "Enter first integer" );
– 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
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41
2.5
20
Another Java Application: Adding
Integers
firstNumber = JOptionPane.showInputDialog( "Enter first integer" );
– 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" )
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42
2.5
23
24
Another Java Application: Adding
Integers
secondNumber =
JOptionPane.showInputDialog( "Enter second integer" );
– Similar to previous statement
• Assigns variable secondNumber to second integer input
27
28
number1 = Integer.parseInt( firstNumber );
number2 = Integer.parseInt( secondNumber );
– 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
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43
2.5
31
Another Java Application: Adding
Integers
sum = number1 + number2;
– 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
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44
2.5
34
35
Another Java Application: Adding
Integers
JOptionPane.showMessageDialog( null, "The sum is " + sum,
"Results", JOptionPane.PLAIN_MESSAGE );
– 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 "
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45
2.5
34
35
Another Java Application: Adding
Integers
JOptionPane.showMessageDialog( null, "The sum is " + sum,
"Results", JOptionPane.PLAIN_MESSAGE );
– 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
2003 Prentice Hall, Inc. All rights reserved.
46
2.5
Another Java Application: Adding
Integers
Messa g e d ia lo g typ e
Ic o n
Desc rip tio n
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
Displays a dialog that simply contains a
message, with no icon.
Fig. 2.12 JOptionPane c o nsta nts fo r m essa g e d ia lo g s.
2003 Prentice Hall, Inc. All rights reserved.
no icon
47
2.5
Another Java Application: Adding
Integers
• Upcoming program
– Use Scanner class to input two values from the console
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48
1
2
3
// Fig. 2.7: Addition.java
// Addition program that displays the sum of two
numbers.
import java.util.Scanner; // program uses class
Scanner
4
5 public class Addition
6 {
7
// main method begins execution of Java application
8
public static void main( String args[] )
9
{
10 // criate Scanner to optain input ftom comment window
11
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 numbers
16
17
System.out.print(“Enter first integer:”);
18
number1 = input.nextInt(); //read first number
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49
19
20
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26
27
28
System.out.print(“Enter second integer:”);
number2 = input.nextInt(); //read first number
sum = number1 + number2
System.out.pritf(“Sum is %d\n”, sum);
}
}
// end of main
// end of calss Addition
The programs output:
Enter first integer 45
Enter second integer 72
Sum is 117
2003 Prentice Hall, Inc. All rights reserved.
50
2.5
Another Java Application: Adding
Integers
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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51
2.5
Another Java Application: Adding
Integers
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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52
2.5
Another Java Application: Adding
Integers
• 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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53
2.5
Another Java Application: Adding
Integers
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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54
2.5
Another Java Application: Adding
Integers
• 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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55
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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56
2.6 Memory Concepts
• Visual Representation
– Sum = 0; number1 = 1; number2 = 2;
sum
0
– Sum = number1 + number2; after execution of statement
sum
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3
57
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 remainder
7 / 5 evaluates to 1
– Remainder operator % returns the remainder
7 % 5 evaluates to 2
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58
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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59
2.7
Operator(s)
*
/
%
+
Fig. 2.12
Operation(s)
Multiplication
Division
Remainder
Addition
Subtraction
Arithmetic
Order of evaluation (precedence)
Evaluated first. If there are several of this type
of operator, they are evaluated from left to
right.
Evaluated next. If there are several of this type
of operator, they are evaluated from left to
right.
Precedence of arithmetic operators.
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60
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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61
Assig nm ent
Sa m p le
Exp la na tion
op era tor
exp ression
Assume: int c = 3,
d = 5, e = 4, f
= 6, g = 12;
+=
c += 7
c = c + 7
-=
d -= 4
d = d - 4
*=
e *= 5
e = e * 5
/=
f /= 3
f = f / 3
%=
g %= 9
g = g % 9
Fig. 4.12 Arithm etic a ssig nm ent op era to rs.
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Assig ns
10 to c
1 to d
20 to e
2 to f
3 to g
62
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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63
Op era tor Ca lled
++
preincrement
++
postincrement
--
predecrement
--
postdecrement
Fig. 4.13 The inc rem ent
2003 Prentice Hall, Inc. All rights reserved.
Sa m p le
exp ression
++a
Exp la na tion
Increment a by 1, then use the new
value of a in the expression in
which a resides.
a++
Use the current value of a in the
expression in which a resides, then
increment a by 1.
--b
Decrement b by 1, then use the
new value of b in the expression in
which b resides.
b-Use the current value of b in the
expression in which b resides, then
decrement b by 1.
a nd d ec re m ent op era tors.
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// Fig. 4.14: Increment.java
// Preincrementing and postincrementing operators.
public class Increment {
Outline
Line 13 postincrements c
public static void main( String args[] )
{
int c;
// demonstrate postincrement
c = 5;
//
System.out.println( c );
//
System.out.println( c++ ); //
System.out.println( c );
//
System.out.println();
assign 5 to c
print 5 Line 21 preincrements
print 5 then postincrement
print 6
Increment.java
Line 13 postincrement
Line 21 preincrement
c
// skip a line
// demonstrate preincrement
c = 5;
//
System.out.println( c );
//
System.out.println( ++c ); //
System.out.println( c );
//
assign 5 to c
print 5
preincrement then print 6
print 6
} // end main
} // end class Increment
5
5
6
5
6
6
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65
Op era tors
Assoc ia tivity
Typ e
++ -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 Prec ed enc e a nd a ssoc ia tivity of the op era tors d isc ussed so fa r.
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66
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
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67
Typ e
boolean
Size in b its
char
16
byte
8
short
16
int
32
long
64
float
32
double
64
Fig. 4.16 The Ja va
Va lues
true or false
Sta nd a rd
[Note: The representation of a boolean is
specific to the Java Virtual Machine on each
computer platform.]
'\u0000' to '\uFFFF'
(ISO Unicode character set)
(0 to 65535)
–128 to +127
(–27 to 27 – 1)
–32,768 to +32,767
(–215 to 215 – 1)
–2,147,483,648 to +2,147,483,647
(–231 to 231 – 1)
–9,223,372,036,854,775,808 to
+9,223,372,036,854,775,807
(–263 to 263 – 1)
Negative range:
(IEEE 754 floating point)
–3.4028234663852886E+38 to
–1.40129846432481707e–45
Positive range:
1.40129846432481707e–45 to
3.4028234663852886E+38
Negative range:
(IEEE 754 floating point)
–1.7976931348623157E+308 to
–4.94065645841246544e–324
Positive range:
4.94065645841246544e–324 to
1.7976931348623157E+308
p rim itive typ es.
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68
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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70
• The output is:
b1 is false
b2 && b3 is false
b2 && b3 is false
b1 is false
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71
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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73
2.8
Decision Making: Equality and
Relational Operators
Sta nd a rd a lg eb ra ic Ja va eq ua lity
Exa m p le
eq ua lity o r
or rela tio na l
of Ja va
rela tiona l o p era tor op era tor
c ond itio n
Equality operators
==
x == y
=
!=
x != y
Relational operators
>
x > y
>
<
x < y
<
>=
x >= y
<=
x <= y
Fig. 2.19 Eq ua lity a nd rela tiona l o p era to rs.
Mea ning o f
Ja va c ond ition
x is equal to y
x is not equal to y
x is greater than y
x is less than y
x is greater than or equal to y
x is less than or equal to y
• Upcoming program uses if statements
– Discussion afterwards
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// Fig. 2.20: Comparison.java
// Compare integers using if statements, relational operators
// and equality operators.
// Java packages
import javax.swing.JOptionPane;
public class Comparison {
Outline
Comparison.java
1. import
// main method begins execution of Java application
public static void main( String args[] )
{
String firstNumber;
// first string entered by user
String secondNumber; // second string entered by user
String result;
// a string containing the output
int number1;
int number2;
74
// first number to compare
// second number to compare
2. Class
Comparison
2.1 main
2.2 Declarations
// read first number from user as a string
firstNumber = JOptionPane.showInputDialog( "Enter first integer:" );
2.3 Input data
(showInputDialo
g)
// read second number from user as a string
secondNumber =
JOptionPane.showInputDialog( "Enter second integer:" );
2.4 parseInt
// convert numbers from type String to type int
number1 = Integer.parseInt( firstNumber );
number2 = Integer.parseInt( secondNumber );
// initialize result to empty String
result = "";
2.5 Initialize result
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47
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59
60
Outline
if ( number1 == number2 )
result = result + number1 + " == " + number2;
if ( number1 != number2 )
result = result + number1 + " != " + number2;
Test for equality, createComparison.java
new string,
assign to result.
if ( number1 < number2 )
result = result + "\n" + number1 + " < " + number2;
if ( number1 > number2 )
result = result + "\n" + number1 + " > " + number2;
if ( number1 <= number2 )
result = result + "\n" + number1 + " <= " + number2;
3. if statements
4.
showMessageDialo
g
if ( number1 >= number2 )
result = result + "\n" + number1 + " >= " + number2;
// Display results
JOptionPane.showMessageDialog( null, result, "Comparison Results",
JOptionPane.INFORMATION_MESSAGE );
} // end method main
} // end class Comparison
Notice use of
JOptionPane.INFORMATION_MESSAGE
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76
Outline
Program Output
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77
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// Fig. 2.20: Comparison.java
// Compare integers using if statements, relational operators
// and equality operators.
// Java packages
import javax.swing.JOptionPane;
public class Comparison {
// main method begins execution of Java application
public static void main( String args[] )
{
String firstNumber; // first string entered by user
String secondNumber; // second string entered by user
String result;
// a string containing the output
int number1;
int number2;
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// first number to compare
// second number to compare
78
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30
31
32
// read first number from user as a string
firstNumber = JOptionPane.showInputDialog( "Enter first integer:" );
// read second number from user as a string
secondNumber =
JOptionPane.showInputDialog( "Enter second integer:" );
// convert numbers from type String to type int
number1 = Integer.parseInt( firstNumber );
number2 = Integer.parseInt( secondNumber );
// initialize result to empty String
result = "";
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34
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37
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40
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49
50
if ( number1 == number2 )
result = result + number1 + " == " + number2;
if ( number1 != number2 )
result = result + number1 + " != " + number2;
if ( number1 < number2 )
result = result + "\n" + number1 + " < " + number2;
if ( number1 > number2 )
result = result + "\n" + number1 + " > " + number2;
if ( number1 <= number2 )
result = result + "\n" + number1 + " <= " + number2;
if ( number1 >= number2 )
result = result + "\n" + number1 + " >= " + number2;
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52
53
// Display results
JOptionPane.showMessageDialog( null, result,
"Comparison Results",
54
JOptionPane.INFORMATION_MESSAGE );
55
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} // end method main
59
60 } // end class Comparison
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81
2.8
Decision Making: Equality and
Relational Operators
– Lines 1-12: Comments, import JOptionPane, begin
class Comparison and main
– Lines 13-18: declare variables
• Can use comma-separated lists instead:
13
14
15
String firstNumber,
secondNumber,
result;
– Lines 21-30: obtain user-input numbers and parses input
string into integer variables
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82
2.8
32
Decision Making: Equality and
Relational Operators
result = "";
– Initialize result with empty string
34
35
if ( number1 == number2 )
result = result + number1 + " == " + number2;
– 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
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83
2.8
Decision Making: Equality and
Relational Operators
– 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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84
2.8
Decision Making: Equality and
Relational Operators
• Precedence of operators
– All operators except for = (assignment) associates from left
to right
• For example: x = y = z is evaluated x = (y = z)
Op era tors
Assoc ia tivity
Typ e
* / %
left to right
multiplicative
+ left to right
additive
< <= > >=
left to right
relational
== !=
left to right
equality
=
right to left
assignment
Fig. 2.21 Prec ed enc e a nd a ssoc ia tivity of the op era tors d isc ussed so fa r.
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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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[grade >= 60]
print “Passed”
[grade < 60]
Fig 4.3 if single-selections statement activity diagram.
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87
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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88
[grade < 60]
print “Failed”
[grade >= 60]
print “Passed”
Fig 4.4 if…else double-selections statement activity diagram.
2003 Prentice Hall, Inc. All rights reserved.
89
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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90
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.
expression1
expression2
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91
expression1 ^
expression2
false
false
false
false
true
true
true
false
true
true
true
false
Fig. 5.17 ^ (boolean logical exclusive OR) operator truth table.
expression1
expression2
expression
!expression
false
true
true
false
Fig. 5.18 ! (logical negation, or logical NOT) operator truth table.
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Outline
// Fig. 5.19: LogicalOperators.java
// Logical operators.
import javax.swing.*;
LogicalOperator
s.java
public class LogicalOperators
public static void main( String args[] )
{
// create JTextArea to display results
JTextArea outputArea = new JTextArea( 17, 20 );
Lines 16-20
Lines 23-27
// attach JTextArea to a JScrollPane so user can scroll results
JScrollPane scroller = new JScrollPane( outputArea );
Conditional AND truth table
// create truth table for && (conditional AND) operator
String output = "Logical AND (&&)" +
"\nfalse && false: " + ( false && false ) +
"\nfalse && true: " + ( false && true ) +
"\ntrue && false: " + ( true && false ) +
"\ntrue && true: " + ( true && true );
Conditional OR truth table
// create truth table for || (conditional OR) operator
output += "\n\nLogical OR (||)" +
"\nfalse || false: " + ( false || false ) +
"\nfalse || true: " + ( false || true ) +
"\ntrue || false: " + ( true || false ) +
"\ntrue || true: " + ( true || true );
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// create truth table for & (boolean logical AND) operator
output += "\n\nBoolean logical AND (&)" +
"\nfalse & false: " + ( false & false ) +
"\nfalse & true: " + ( false & true ) +
"\ntrue & false: " + ( true & false ) +
Boolean logical
"\ntrue & true: " + ( true & true );
Outline
AND
LogicalOperator
s.java
truth table
Lines
// create truth table for | (boolean logical inclusive OR) operator
output += "\n\nBoolean logical inclusive OR (|)" +
"\nfalse | false: " + ( false | false ) +
Lines
"\nfalse | true: " + ( false | true ) +
"\ntrue | false: " + ( true | false ) +
Boolean logical inclusive
Lines
"\ntrue | true: " + ( true | true );
30-34
37-41
44-48
OR truth table
// create truth table for ^ (boolean logical exclusive OR) operator
Lines
output += "\n\nBoolean logical exclusive OR (^)" +
"\nfalse ^ false: " + ( false ^ false ) +
"\nfalse ^ true: " + ( false ^ true ) +
"\ntrue ^ false: " + ( true ^ false ) +
Boolean logical exclusive
"\ntrue ^ true: " + ( true ^ true );
51-53
OR truth table
// create truth table for ! (logical negation) operator
output += "\n\nLogical NOT (!)" +
"\n!false: " + ( !false ) +
"\n!true: " + ( !true );
Logical NOT truth
outputArea.setText( output );
table
// place results in JTextArea
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JOptionPane.showMessageDialog( null, scroller,
"Truth Tables", JOptionPane.INFORMATION_MESSAGE );
System.exit( 0 );
// terminate application
} // end main
94
Outline
LogicalOperator
s.java
} // end class LogicalOperators
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95
Operators
Associativity
Type
++ -right to left
unary postfix
++ -- +
!
right to left
unary
(type)
*
/
%
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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96
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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97
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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98
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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99
• 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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100
•
•
•
•
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
2003 Prentice Hall, Inc. All rights reserved.
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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102
2000
1900
C year mode 400=0
B year mode 100 = 0
2004
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A. Year mode 4 = 0
103
• 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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104
• 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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105
• 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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106
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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107
• 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
2003 Prentice Hall, Inc. All rights reserved.
