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CS 335 Java Programming – GUI and Swing

Java: Basic GUI Components      

Swing component overview Event handling Inner classes and anonymous inner classes Examples and various components Layouts Panels

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Alternatives  

AWT (almost obsolete now) SWT (The Standard Widget Toolkit) – – –

Open source from IBM Using native window calls – fast response Very much like MFC

Swing Components 

Lightweight vs. heavyweight components: – –



Lightweight: platform independent Heavyweight: tied to platform; windowing system

Swing components are lightweight

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Superclasses of Swing’s Lightweight GUI Components 

Common lightweight component features – – – – –

Pluggable look-and-feel to customize the appearance of components Shortcut keys (called mnemonics) Common event-handling capabilities Brief description of component’s purpose (called tool tips) Support for localization 5

A Java Screen Layout

Frame  JFrame Menu Bar (optional) Content Pane

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import java.awt.*; import java.awt.event.*; import javax.swing.*; public class FrameDemo { public static void main(String s[]) { JFrame frame = new JFrame("FrameDemo"); frame.addWindowListener(new WindowAdapter() { public void windowClosing(WindowEvent e) { System.exit(0); } }); JLabel myLabel = new JLabel(“Hello World"); myLabel.setPreferredSize(new Dimension(175, 100)); frame.getContentPane().add(myLabel, BorderLayout.CENTER); frame.pack(); frame.setVisible(true); // show() is “deprecated” } }

Choose Look and Feel 

Only available under Swing

try { UIManager.setLookAndFeel( UIManager.getCrossPlatformLookAndFeelClassName()); } catch (Exception e) { } Always give me the java look! Ref: available look and feel at http://java.sun.com/docs/books/tutorial/uiswing/misc/plaf.html

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The Event Handing Model  

GUI components are event-driven Programmer must – –

 

register events implement event handlers

Event registration: add “listeners” Event implementation: define listener methods

3 Steps for an Event Handler 1.

either implements a listener interface or extends a class that implements a listener interface public class MyClass implements ActionListener {

2.

Register your listener someComponent. addActionListener(instanceOfMyClass);

3.

Implement user action public void actionPerformed(ActionEvent e) { ...//code that reacts to the action... }

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Example: Registering Events public class TextFieldTest extends JFrame { private JTextField text1, text2, text3; private JPasswordField password; public TextFieldTest() { super( "Testing JTextField and JPasswordField" ); Container c = getContentPane(); c.setLayout( new FlowLayout() ); // construct textfield with default sizing text1 = new JTextField( 10 ); c.add( text1 ); // construct textfield with default text text2 = new JTextField( "Enter text here" ); c.add( text2 );

// construct textfield with default text and // 20 visible elements and no event handler text3 = new JTextField( "Uneditable text field", 20 ); text3.setEditable( false ); c.add( text3 ); // construct textfield with default text password = new JPasswordField( "Hidden text" ); c.add( password ); TextFieldHandler handler = new TextFieldHandler(); text1.addActionListener( handler ); text2.addActionListener( handler ); text3.addActionListener( handler ); password.addActionListener( handler ); setSize( 325, 100 ); show(); }

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Event Registration

Listeners for Event Types        

ActionListener MouseListener MouseMotionListener KeyListener ButtonChangeListener AncestorListener PropertyChangeListener ...

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Example: Handling Events // inner class for event handling private class TextFieldHandler implements ActionListener { public void actionPerformed( ActionEvent e ) { String s = ""; if ( e.getSource() == text1 ) s = "text1: " + e.getActionCommand(); else if ( e.getSource() == text2 ) s = "text2: " + e.getActionCommand(); else if ( e.getSource() == text3 ) s = "text3: " + e.getActionCommand(); else if ( e.getSource() == password ) { JPasswordField pwd = (JPasswordField) e.getSource(); s = "password: " + new String( pwd.getPassword() ); } JOptionPane.showMessageDialog( null, s ); }

Driver for Example public static void main( String args[] ) { TextFieldTest app = new TextFieldTest(); app.addWindowListener( new WindowAdapter() { public void windowClosing( WindowEvent e ) { System.exit( 0 ); } } ); }

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Event Handling and Inner Classes  

Event handler classes are usually private Often event handlers are anonymous inner classes defined purely to implement the handing method: app.addWindowListener( new WindowAdapter() { public void windowClosing( WindowEvent e ) { System.exit( 0 ); } } );

GUI Components http://java.sun.com/docs/books/tutorial/uiswing/components/components.html

For example  JTextField and JPasswordField  JButton  JCheckBox and JRadioButton  JComboBox  JList and Multiple Selection Lists

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JTextField and JPasswordField

JButton

public class ButtonTest extends JFrame { private JButton plainButton, fancyButton; public ButtonTest() { super( "Testing Buttons" ); Container c = getContentPane(); c.setLayout( new FlowLayout() ); // create buttons plainButton = new JButton( "Plain Button" ); c.add( plainButton );

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Icon bug1 = new ImageIcon( "bug1.gif" ); Icon bug2 = new ImageIcon( "bug2.gif" ); fancyButton = new JButton( "Fancy Button", bug1 ); fancyButton.setRolloverIcon( bug2 ); c.add( fancyButton ); // create an instance of inner class ButtonHandler // to use for button event handling ButtonHandler handler = new ButtonHandler(); fancyButton.addActionListener( handler ); plainButton.addActionListener( handler ); setSize( 275, 100 ); show(); }

public static void main( String args[] ) { ButtonTest app = new ButtonTest(); app.addWindowListener( new WindowAdapter() { public void windowClosing( WindowEvent e ) { System.exit( 0 ); } } ); // or NEW for ver 1.3 of java 2 // frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); } // inner class for button event handling private class ButtonHandler implements ActionListener { public void actionPerformed( ActionEvent e ) { JOptionPane.showMessageDialog( null, "You pressed: " + e.getActionCommand() ); } } }

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Mouse Event Handling 

Mouse events – –

– –

Create a MouseEvent object Handled by MouseListeners and MouseMotionListeners MouseInputListener combines the two interfaces Interface MouseWheelListener declares method mouseWheelMoved to handle MouseWheelEvents 23

Event Handling: The Mouse      

mousePressed mouseClicked mouseReleased mouseEntered, mouseExited mouseDragged mouseMoved

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Note 

Method calls to mouseDragged and mouseReleased are sent to the MouseMotionListener for the Component on which a mouse drag operation started. Similarly, the mouseReleased method call at the end of a drag operation is sent to the MouseListener for the Component on which the drag operation started.

// Fig. 12.17: MouseTracker.java // Demonstrating mouse events. import java.awt.*; import java.awt.event.*; import javax.swing.*; public class MouseTracker extends JFrame implements MouseListener, MouseMotionListener { private JLabel statusBar; public MouseTracker() { super( "Demonstrating Mouse Events" ); statusBar = new JLabel(); getContentPane().add( statusBar, BorderLayout.SOUTH ); // application listens to its own mouse events addMouseListener( this ); addMouseMotionListener( this ); setSize( 275, 100 ); show(); }

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// MouseListener event handlers public void mouseClicked( MouseEvent e ) { statusBar.setText( "Clicked at [" + e.getX() + ", " + e.getY() + "]" ); } public void mousePressed( MouseEvent e ) { statusBar.setText( "Pressed at [" + e.getX() + ", " + e.getY() + "]" ); } public void mouseReleased( MouseEvent e ) { statusBar.setText( "Released at [" + e.getX() + ", " + e.getY() + "]" ); } public void mouseEntered( MouseEvent e ) { statusBar.setText( "Mouse in window" ); } public void mouseExited( MouseEvent e ) { statusBar.setText( "Mouse outside window" ); }

// MouseMotionListener event handlers public void mouseDragged( MouseEvent e ) { statusBar.setText( "Dragged at [" + e.getX() + ", " + e.getY() + "]" ); } public void mouseMoved( MouseEvent e ) { statusBar.setText( "Moved at [" + e.getX() + ", " + e.getY() + "]" ); } public static void main( String args[] ) { MouseTracker app = new MouseTracker(); app.addWindowListener( new WindowAdapter() { public void windowClosing( WindowEvent e ) { System.exit( 0 ); } } ); } }

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Adapter Classes   

Interfaces with many methods to implement can be cumbersome The adapter class provides a default implementation of all interface methods Application can over-ride interface methods that are of interest

Adapter Classes 

Adapter class – –

Implements event listener interface Provides default implementation for all eventhandling methods

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Software Engineering Observation 11.7 

When a class implements an interface, the class has an “is a” relationship with that interface. All direct and indirect subclasses of that class inherit this interface. Thus, an object of a class that extends an eventadapter class is an object of the corresponding event-listener type (e.g., an object of a subclass of MouseAdapter is a MouseListener).

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Extending MouseAdapter 

MouseAdapter – –

Adapter class for MouseListener and MouseMotionListener interfaces Extending class allows you to override only the methods you wish to use

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Adapter Classes Event-adapter class in java.awt.event

Implements interface

ComponentAdapter ContainerAdapter FocusAdapter KeyAdapter MouseAdapter MouseMotionAdapter WindowAdapter

ComponentListener ContainerListener FocusListener KeyListener MouseListener MouseMotionListener WindowListener

// Fig. 12.19: Painter.java // Using class MouseMotionAdapter. import javax.swing.*; import java.awt.event.*; import java.awt.*; public class Painter extends JFrame { private int xValue = -10, yValue = -10; public Painter() { super( "A simple paint program" ); getContentPane().add( new Label( "Drag the mouse to draw" ), BorderLayout.SOUTH ); addMouseMotionListener( new MouseMotionAdapter() { public void mouseDragged( MouseEvent e ) { xValue = e.getX(); Inner Class yValue = e.getY(); repaint(); } } ); setSize( 300, 150 ); show(); }

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public void paint( Graphics g ) { g.fillOval( xValue, yValue, 4, 4 ); } public static void main( String args[] ) { Painter app = new Painter(); app.addWindowListener( new WindowAdapter() { public void windowClosing( WindowEvent e ) { System.exit( 0 ); } } ); } }

Using an Anonymous Inner Class for Event Handling 

Anonymous inner class – – – –

Special form of inner class Declared without a name Typically appears inside a method call Has limited access to local variables

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Swing Component Demo  

Try This http://java.sun.com/docs/books/tutorial/uiswin g/examples/components/index.html

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