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Introduction To Java GUI

Simplest GUI programming:

JOptionPane

An option pane is a simple dialog box for graphical input/output

• advantages: - (^) simple - (^) flexible (in some ways) - looks better than the black box of doom

• (^) disadvantages:

   created with static methods; 

not very object-oriented

• (^) not very powerful (just simple dialog boxes)

JOptionPane examples 1

• showMessageDialog analogous to

System.out.println for displaying a simple

message

import javax.swing.*;

class MessageDialogExample {

public static void main(String[] args) {

JOptionPane.showMessageDialog(null,

"How's the weather?");

JOptionPane.showMessageDialog(null,

"Second message");

}

}

JOptionPane examples 2

• showConfirmDialog analogous to a

System.out.print that prints a question, then reading

an input value from the user (can only be one of the provided

choices)

import javax.swing.*;

class ConfirmDialogExample {

public static void main(String[] args) {

int choice = JOptionPane.showConfirmDialog(null,

"Erase your hard disk?");

if (choice == JOptionPane.YES_OPTION) {

JOptionPane.showMessageDialog(null, "Disk erased!");

} else {

JOptionPane.showMessageDialog(null, "Cancelled.");

}

}

}

Swing Overview

• (^) Swing component inheritance hierarchy

   Component defines methods that can be used in its subclasses 

(for example, paint and repaint)

• Container - collection of related components - (^) When using JFrames, attach components to the content

pane (a Container)

• Method add to add components to content pane

JComponent - superclass to most Swing components

• (^) Much of a component's functionality inherited from these

classes

java.awt.Component

java.awt.Container

java.lang.Object

javax.swing.JComponent

JLabel

• Labels - Provide text instructions on a GUI - Read-only text - (^) Programs rarely change a label's contents - (^) Class JLabel (subclass of JComponent)
• (^) Methods
  • (^) Can declare label text in constructor
  • myLabel.setToolTipText( "Text" ) - (^) Displays "Text"in a tool tip when mouse over label
  • myLabel.setText( "Text" )
  • myLabel.getText()

1. import

1.1 extend JFrame

1.2 Declarations

1.3 Create container to

hold labels

1.4 Initialize JLabels

1 // Fig. 29.4: LabelTest.java

2 // Demonstrating the JLabel class.

3 import javax.swing.*;

4 import java.awt.*;

5 import java.awt.event.*;

7 public class LabelTest extends JFrame {

8 private JLabel label1, label2, label3;

10 public LabelTest()

12 super( "Testing JLabel" );

14 Container c = getContentPane();

15 c.setLayout( new FlowLayout() );

17 // JLabel constructor with a string argument

18 label1 = new JLabel( "Label with text" );

19 label1.setToolTipText( "This is label1" );

20 c.add( label1 );

22 // JLabel constructor with string, Icon and

23 // alignment arguments

24 Icon bug = new ImageIcon( "bug1.gif" );

25 label2 = new JLabel( "Label with text and icon",

26 bug, SwingConstants.LEFT );

27 label2.setToolTipText( "This is label2" );

28 c.add( label2 );

30 // JLabel constructor no arguments

1.4 Initialize JLabels

31 label3 = new JLabel();

32 label3.setText( "Label with icon and text at bottom" );

33 label3.setIcon( bug );

34 label3.setHorizontalTextPosition(

35 SwingConstants.CENTER );

36 label3.setVerticalTextPosition(

37 SwingConstants.BOTTOM );

38 label3.setToolTipText( "This is label3" );

39 c.add( label3 );

41 setSize( 275, 170 );

42 show();

45 public static void main( String args[] )

47 LabelTest app = new LabelTest();

JTextArea

• Area for manipulating multiple lines of text - Like JTextField, inherits from JTextComponent - Many of the same methods
• JScrollPane - Provides scrolling - Initialize with component - new JScrollPane( myComponent ) - Can set scrolling policies (always, as needed, never) - (^) See book for details

JTextArea

• Box container - Uses BoxLayout layout manager - (^) Arrange GUI components horizontally or vertically - Box b = Box.createHorizontalbox(); - Arranges components attached to it from left to right, in order

attached

2. main

31 t2.setText( t1.getSelectedText() );

35 b.add( copy );

37 t2 = new JTextArea( 10, 15 );

38 t2.setEditable( false );

39 b.add( new JScrollPane( t2 ) );

41 Container c = getContentPane();

42 c.add( b );

43 setSize( 425, 200 );

44 show();

47 public static void main( String args[] )

49 TextAreaDemo app = new TextAreaDemo();

Program Output

JTextField and JPasswordField

• (^) Methods (continued)

   setEditable( boolean ) - (^) If true, user can edit text 

  • getPassword - (^) Class JPasswordField - (^) Returns password as an array of type char
• Example - Create JTextFields and a JPasswordField - Create and register an event handler - (^) Displays a dialog box when Enter pressed

JButton

• Button - Component user clicks to trigger an action - (^) Several types of buttons - (^) Command buttons, toggle buttons, check boxes, radio buttons
• Command button - Generates ActionEvent when clicked - Created with class JButton - (^) Inherits from class AbstractButton
• Jbutton - (^) Text on face called button label - Each button should have a different label - Support display of Icons