Java: GUI

Introduction Graphical User Interface (GUI) Gives program distinctive “look” and “feel” Provides users with basic level of familiarity Built from GUI components (controls, widgets, etc.) User interacts with GUI component via mouse, keyboard, etc.

GUI Programming Concepts in Java Java GUI ("Swing") has components Windows GUI has controls Unix GUI has widgets examples: labels, buttons, check boxes, radio buttons, text input boxes, pull down lists Java Swing components: JLabel, JButton, JCheckBox, JRadioButton, JTextField, JTextArea, JComboBox

Java GUI history: the AWT AWT(JDK 1.0, 1.1): Abstract Window Toolkit package: java.awt, java.awt.event heavyweight components using native GUI system elements used for applets until most browsers supported JRE 1.2

Swing in Java Swing(Java 2, JDK 1.2+) lightweight components that do not rely on the native GUI or OS “ look and feel” of Swing components are identical on different platforms can be customized Swing inherits from AWT AWT still used for events, layouts

Swing Components in Java advanced GUI support. e.g. drag-and-drop package names: javax.swing, javax.swing.event components inherit from JComponent components are added to a top-level container: JFrame, JDialog, or JApplet.

Lightweight vs. Heavyweight GUI Components Lightweight components Not tied directly to GUI components supported by underlying platform Heavyweight components Tied directly to the local platform AWT components Some Swing components

Basic GUI Programming Steps in Java declare a container and components add components to one or more containers using a layout manager register event listener(s) with the components create event listener method(s)

AWT Event Class Hierarchy EventObject AWTEvent ActionEvent ComponentEvent AdjustmentEvent TextEvent ItemEvent ContainerEvent MouseEvent keyEvent FocusEvent InputEvent PaintEvent WindowEvent

AWT Events Component Event Generated Generate When Button ActionEvent Clicked Selected or deselected Moved, resized, hidden or shown Checkbox CheckboxMenuItem Gained or loses fccus Pressed or released ComponentEvent Component Double Clicked ItemEvent Container ContainerEvent Added or removed ItemEvent ItemEvent Selected or deselected Selected or deselected Choice FocusEvent KeyEvent List ActionEvent ItemEvent Selected or deselected Selected ActionEvent MenuItem Moved AdjustmentEvent Scrollbar Changed TextEvent TextComponent Completed editing TextEvent TextField Opened, closed, iconified, deiconified, etc. WindowEvent Window

Events Delegation Model User Action Source Object Triggering an event Target/Listener Object Event Object Registering for an event Creating an event Notify Event Listener Handle event Event Handler

Swing Overview Swing GUI components Package javax.swing Components originate from AWT (package java.awt ) Contain look and feel Appearance and how users interact with program Lightweight components Written completely in Java

12.2 Swing Overview (cont.) Class Component Contains method paint for drawing Component onscreen Class Container Collection of related components Contains method add for adding components Class JComponent Pluggable look and feel for customizing look and feel Shortcut keys ( mnemonics ) Common event-handling capabilities

Fig. 12.3 Common superclasses of many of the Swing components.

12.3 JLabel Label Provide text on GUI Defined with class JLabel Can display: Single line of read-only text Image Text and image

1 // Fig. 12.4: LabelTest.java 2 // Demonstrating the JLabel class. 3 4 // Java core packages 5 import java.awt.*; 6 import java.awt.event.*; 7 8 // Java extension packages 9 import javax.swing.*; 10 11 public class LabelTest extends JFrame { 12 private JLabel label1, label2, label3; 13 14 // set up GUI 15 public LabelTest() 16 { 17 super ( "Testing JLabel" ); 18 19 // get content pane and set its layout 20 Container container = getContentPane(); 21 container.setLayout( new FlowLayout() ); 22 23 // JLabel constructor with a string argument 24 label1 = new JLabel( "Label with text" ); 25 label1.setToolTipText( "This is label1" ); 26 container.add( label1 ); 27 28 // JLabel constructor with string, Icon and 29 // alignment arguments 30 Icon bug = new ImageIcon( "bug1.gif" ); 31 label2 = new JLabel( "Label with text and icon" , 32 bug, SwingConstants. LEFT ); 33 label2.setToolTipText( "This is label2" ); 34 container.add( label2 ); 35 LabelTest.java Line 12 Line 24 Line 25 Lines 31-32 Declare three JLabel s Create first JLabel with text “ Label with text ” Create second JLabel with text to left of image Tool tip is text that appears when user moves cursor over JLabel

36 // JLabel constructor no arguments 37 label3 = new JLabel(); 38 label3.setText( "Label with icon and text at bottom" ); 39 label3.setIcon( bug ); 40 label3.setHorizontalTextPosition( SwingConstants. CENTER ); 41 label3.setVerticalTextPosition( SwingConstants. BOTTOM ); 42 label3.setToolTipText( "This is label3" ); 43 container.add( label3 ); 44 45 setSize( 275 , 170 ); 46 setVisible( true ); 47 } 48 49 // execute application 50 public static void main( String args[] ) 51 { 52 LabelTest application = new LabelTest(); 53 54 application.setDefaultCloseOperation( 55 JFrame. EXIT_ON_CLOSE ); 56 } 57 58 } // end class LabelTest LabelTest.java Lines 37-41 Create third JLabel with text below image

12.4 Event-Handling Model GUIs are event driven Generate events when user interacts with GUI e.g., moving mouse, pressing button, typing in text field, etc. Class java.awt.AWTEvent

Fig. 12.5 Some event classes of package java.awt.event

12.4 Event-Handling Model (cont.) Event-handling model Three parts Event source GUI component with which user interacts Event object Encapsulates information about event that occurred Event listener Receives event object when notified, then responds Programmer must perform two tasks Register event listener for event source Implement event-handling method (event handler)

Fig. 12.6 Event-listener interfaces of package java.awt.event

12.5 JTextField and JPasswordField JTextField Single-line area in which user can enter text JPasswordField Extends JTextField Hides characters that user enters

1 // Fig. 12.7: TextFieldTest.java 2 // Demonstrating the JTextField class. 3 4 // Java core packages 5 import java.awt.*; 6 import java.awt.event.*; 7 8 // Java extension packages 9 import javax.swing.*; 10 11 public class TextFieldTest extends JFrame { 12 private JTextField textField1, textField2, textField3; 13 private JPasswordField passwordField; 14 15 // set up GUI 16 public TextFieldTest() 17 { 18 super ( "Testing JTextField and JPasswordField" ); 19 20 Container container = getContentPane(); 21 container.setLayout( new FlowLayout() ); 22 23 // construct textfield with default sizing 24 textField1 = new JTextField( 10 ); 25 container.add( textField1 ); 26 27 // construct textfield with default text 28 textField2 = new JTextField( "Enter text here" ); 29 container.add( textField2 ); 30 31 // construct textfield with default text and 32 // 20 visible elements and no event handler 33 textField3 = new JTextField( "Uneditable text field" , 20 ); 34 textField3.setEditable( false ); 35 container.add( textField3 ); TextFieldTest.java Lines 12-13 Line 24 Line 28 Lines 33-34 Declare three JTextField s and one JPasswordField First JTextField contains empty string Second JTextField contains text “ Enter text here ” Third JTextField contains uneditable text

36 37 // construct textfield with default text 38 passwordField = new JPasswordField( "Hidden text" ); 39 container.add( passwordField ); 40 41 // register event handlers 42 TextFieldHandler handler = new TextFieldHandler(); 43 textField1.addActionListener( handler ); 44 textField2.addActionListener( handler ); 45 textField3.addActionListener( handler ); 46 passwordField.addActionListener( handler ); 47 48 setSize( 325 , 100 ); 49 setVisible( true ); 50 } 51 52 // execute application 53 public static void main( String args[] ) 54 { 55 TextFieldTest application = new TextFieldTest(); 56 57 application.setDefaultCloseOperation( 58 JFrame. EXIT_ON_CLOSE ); 59 } 60 61 // private inner class for event handling 62 private class TextFieldHandler implements ActionListener { 63 64 // process text field events 65 public void actionPerformed( ActionEvent event ) 66 { 67 String string = "" ; 68 69 // user pressed Enter in JTextField textField1 70 if ( event.getSource() == textField1 ) TextFieldTest.java Line 38 Lines 43-46 Line 62 Line 65 JPasswordField contains text “ Hidden text ,” but text appears as series of asterisks ( * ) Every TextFieldHandler instance is an ActionListener Register GUI components with TextFieldHandler (register for ActionEvent s) Method actionPerformed invoked when user presses Enter in GUI field

71 string = "textField1: " + event.getActionCommand(); 72 73 // user pressed Enter in JTextField textField2 74 else if ( event.getSource() == textField2 ) 75 string = "textField2: " + event.getActionCommand(); 76 77 // user pressed Enter in JTextField textField3 78 else if ( event.getSource() == textField3 ) 79 string = "textField3: " + event.getActionCommand(); 80 81 // user pressed Enter in JTextField passwordField 82 else if ( event.getSource() == passwordField ) { 83 JPasswordField pwd = 84 ( JPasswordField ) event.getSource(); 85 string = "passwordField: " + 86 new String( passwordField.getPassword() ); 87 } 88 89 JOptionPane.showMessageDialog( null , string ); 90 } 91 92 } // end private inner class TextFieldHandler 93 94 } // end class TextFieldTest TextFieldTest.java

12.5.1 How Event Handling Works Two open questions from Section 12.4 How did event handler get registered? Answer: Through component’s method addActionListener Lines 43-46 of TextFieldTest.java How does component know to call actionPerformed ? Answer: Event is dispatched only to listeners of appropriate type Each event type has corresponding event-listener interface Event ID specifies event type that occurred

Fig 12.8 Event registration for JTextField textField1 .

12.6 JButton Button Component user clicks to trigger a specific action Several different types Command buttons Check boxes Toggle buttons Radio buttons javax.swing.AbstractButton subclasses Command buttons are created with class JButton Generate ActionEvent s when user clicks button

Fig. 12.9 The button heirarchy.

1 // Fig. 12.10: ButtonTest.java 2 // Creating JButtons. 3 4 // Java core packages 5 import java.awt.*; 6 import java.awt.event.*; 7 8 // Java extension packages 9 import javax.swing.*; 10 11 public class ButtonTest extends JFrame { 12 private JButton plainButton, fancyButton; 13 14 // set up GUI 15 public ButtonTest() 16 { 17 super ( "Testing Buttons" ); 18 19 // get content pane and set its layout 20 Container container = getContentPane(); 21 container.setLayout( new FlowLayout() ); 22 23 // create buttons 24 plainButton = new JButton( "Plain Button" ); 25 container.add( plainButton ); 26 27 Icon bug1 = new ImageIcon( "bug1.gif" ); 28 Icon bug2 = new ImageIcon( "bug2.gif" ); 29 fancyButton = new JButton( "Fancy Button" , bug1 ); 30 fancyButton.setRolloverIcon( bug2 ); 31 container.add( fancyButton ); 32 33 // create an instance of inner class ButtonHandler 34 // to use for button event handling 35 ButtonHandler handler = new ButtonHandler(); ButtonTest.java Line 12 Line 24 Lines 27-30 Line 35 Create two references to JButton instances Instantiate JButton with text Instantiate JButton with image and rollover image Instantiate ButtonHandler for JButton event handling

36 fancyButton.addActionListener( handler ); 37 plainButton.addActionListener( handler ); 38 39 setSize( 275 , 100 ); 40 setVisible( true ); 41 } 42 43 // execute application 44 public static void main( String args[] ) 45 { 46 ButtonTest application = new ButtonTest(); 47 48 application.setDefaultCloseOperation( 49 JFrame. EXIT_ON_CLOSE ); 50 } 51 52 // inner class for button event handling 53 private class ButtonHandler implements ActionListener { 54 55 // handle button event 56 public void actionPerformed( ActionEvent event ) 57 { 58 JOptionPane.showMessageDialog( null , 59 "You pressed: " + event.getActionCommand() ); 60 } 61 62 } // end private inner class ButtonHandler 63 64 } // end class ButtonTest ButtonTest.java Lines 36-37 Lines 56-60 Register JButton s to receive events from ButtonHandler When user clicks JButton , ButtonHandler invokes method actionPerformed of all registered listeners

Java: GUI

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Java: GUI