Unit 14 1

Further GUI Programming

• Learning Outcomeso Extend examples presented to write more useful applications.

o Write non-trivial, event-driven GUI applications.

• Introduction

• Example 1: Enhancing the Telephone Handset Example

• Example 2: Menu Test

• Self-check Exercise 1

• Example 3: File Dialog Test

• Example 4: Popup Menu Test

• Self-check Exercise 2

• Exercises

Unit 14 2

Introduction

• This is our concluding session on GUIs and event-driven programming.

• In our discussion on GUI-based programs so far, we have covered:

– GUI design issues, GUI components and containers.

– Basic event handling.

– Basic layout management.

• We now cover typical GUI elements found in Windows environment including:

– Menus and pop-up menus

– File dialogs

– Mnemonics and keyboard accelerator

• With this coverage the student's knowledge base of the basics would

• be broadened.

Unit 14 3

Introduction to Example 1

• This example builds on Example 4 of the preceding section.

• Example 4 of the preceding section developed a simple GUI for a

telephone handset.

• We will now add event-handling code to display typed numbers.

• Here is a sample output of the program:

Unit 14 4

Example 1: The Telephone Handset

1 import java.awt.*; import javax.swing.*; import java.awt.event.*; 2 class TelephoneTest extends TestGridBagLayout 3 implements ActionListener{ 4 public TelephoneTest(){ 5 Component components[] = getContentPane().getComponents(); 6 JPanel cancelPanel = (JPanel)components[13]; 7 JButton cancel = (JButton)cancelPanel.getComponent(0); 8 for(int i=0;i<components.length; i++){ 9 if(components[i] instanceof JButton)10 ((JButton)components[i]).addActionListener(this);11 }12 cancel.addActionListener(this);13 }14 public void actionPerformed(ActionEvent ae) {15 if (ae.getActionCommand().equals("Cancel"))16 display.setText("");17 else18 display.setText(display.getText()+ae.getActionCommand());19 }20 public static void main(String [] args){21 new TelephoneTest().setVisible(true);22 }}

Unit 14 5

Introduction to Example 2

• In this example we demonstrate how menus, separator,

mnemonic and accelerators can be added into an

application.

• The output of the example is as follows:

Unit 14 6

Class Hierarchy for Menus

• Classes used to define menus are:

o JMenuBar

o JMenuItem

o JMenu

o JCheckButtonMenuItem

o JRadioButtonMenuItem

Unit 14 7

Details of Program Output

Unit 14 8

Example 2: Menus and Mnemonics

1 import java.awt.event.*; 2 import javax.swing.*; 3 class MenuTest extends JFrame { 4 private JMenuBar menuBar = new JMenuBar(); 5 protected JMenu fileMenu = new JMenu("File"); 6 protected JMenuItem neW, open, quit, save, print; 7 private JMenuItem saveCurrent, saveAs, saveAll; 8 MenuTest(String title){ 9 super(title);10 setJMenuBar(menuBar);11 menuBar.add(fileMenu);12 fileMenu.setMnemonic('F');13 fileMenu.add(neW = new JMenuItem ("New"));14 fileMenu.add(open = new JMenuItem ("Open"));15 open.setMnemonic('o');16 fileMenu.add(save = new JMenu ("Save"));17 save.add(saveCurrent = new JMenuItem ("Save Current"));18 save.add(saveAs = new JMenuItem ("Save As"));19 save.add(saveAll = new JMenuItem ("Save All"));20 fileMenu.add(save);21 fileMenu.add(print = new JCheckBoxMenuItem ("Print"));22 fileMenu.addSeparator();

Unit 14 9

Menus and Mnemonics (cont’d)

23 fileMenu.add(quit = new JMenuItem("Quit"));24 quit.setMnemonic(KeyEvent.VK_Q);25 quit.setAccelerator(26 KeyStroke.getKeyStroke(KeyEvent.VK_Q,KeyEvent.CTRL_MASK));27 quit.addActionListener(new ActionListener(){28 public void actionPerformed(ActionEvent e){29 int result=JOptionPane.showConfirmDialog(MenuTest.this,30 "Quit/Close Menu Demos Window?");31 if (result == JOptionPane.YES_OPTION)32 System.exit(0);33 }34 });35 setSize(300,300);36 }37 public static void main(String args[]){38 MenuTest t = new MenuTest("Menus Test");39 t.setVisible(true);40 }41 }

Unit 14 10

Introduction to Example 3

• This example extends Example 2 to launch a file dialog on selecting

the Open menu.

• The selected file name is simply printed on another display window.

• The output is as follows:

Unit 14 11

Example 3: File Dialog Test

1 import java.awt.*; 2 import java.awt.event.*; 3 import javax.swing.*; 4 class FileDialogTest extends MenuTest { 5 JEditorPane textPane= new JEditorPane(); 6 FileDialogTest(String title){ 7 super(title); 8 open.addActionListener( new ActionListener() { 9 public void actionPerformed(ActionEvent e ) {10 FileDialog fd = new FileDialog(FileDialogTest.this);11 fd.setVisible(true);12 textPane.setText("Selected file: "+fd.getFile());13 } });14 getContentPane().add(textPane);15 }16 public static void main(String args[]){17 FileDialogTest t = new FileDialogTest("File Dialog Test");18 t.setVisible(true);1920 }21 }

Unit 14 12

Introduction to Example 4

• This example extends Example 2 of the preceding section to add pop-up menus..

• The output looks like:

• The menu consists of three colors that can be used to reset a component’s background color.

Unit 14 13

Example 4: Popup Menu Test

1 import java.awt.*; import java.awt.event.*; import javax.swing.*; 2 public class PopupMenuTest extends TestGridLayout{ 3 Component selectedComponent; 4 JPopupMenu colorMenu = new JPopupMenu(); 5 JMenuItem blue, white, yellow; 6 public PopupMenuTest(){ 7 setTitle("Popup Menu Test"); 8 colorMenu.add(blue=new JMenuItem("Blue")); 9 colorMenu.add(white=new JMenuItem("White"));10 colorMenu.add(yellow=new JMenuItem("Yellow"));11 Component components[] = getContentPane().getComponents();12 class MyListener extends MouseAdapter {13 public void mousePressed(MouseEvent e){checkPopup(e);}14 public void mouseClicked(MouseEvent e){checkPopup(e);}15 public void mouseReleased(MouseEvent e){checkPopup(e);}16 public void checkPopup(MouseEvent e) {17 if (e.isPopupTrigger()){18 selectedComponent = e.getComponent();19 colorMenu.show(e.getComponent(),e.getX(),e.getY());20 }21 }22 }

Unit 14 14

Popup Menu Test (cont’d)

23 MouseListener mylistener = new MyListener();24 for(int i=0;i<components.length-1; i++){25 JButton b = (JButton)components[i];26 b.addMouseListener(mylistener);27 }28 blue.addActionListener(new ActionListener () {29 public void actionPerformed(ActionEvent ae){30 selectedComponent.setBackground(Color.blue);31 }});32 white.addActionListener(new ActionListener() {33 public void actionPerformed(ActionEvent ae){34 selectedComponent.setBackground(Color.white);35 }});36 yellow.addActionListener(new ActionListener() {37 public void actionPerformed(ActionEvent ae){38 selectedComponent.setBackground(Color.yellow);39 }});40 }41 public static void main(String[] args) {42 new PopupMenuTest().setVisible(true);43 }44 }

Unit 14 15

Review Exercises

1 What are the event sources and event listeners in Example 1?2 Can the event handler in Example 1 be implemented in a single anonymous

class? If not, why not?3 Modify Example 1 to use two inner classes instead of one. Can the two inner

classes both be anonymous? Is the program with one inner class better than the one with two? Explain.

4 Enhance Example 1 so that when the Redial button is pushed the last text displayed on the text component is displayed again.

5 Write a Java program to illustrate how a component event can be handled. 6 Modify Example 3 so that when a file is double-clicked from the file dialog

indow the file is opened rather than displaying its name in the editor pane.7 When you run Example 4, you will find that the lower part of the window is not

responding to the popup menu. Modify this program to ensure that that part of the window also responds to the popup menu events like the buttons in the window.