JDesktopPane and JInternalFrame
Many of today's applications use a multiple-document interface (MDI)a main window (called the parent window) containing other windows (called child windows), to manage several open documents that are being processed in parallel. For example, many e-mail programs allow you to have several windows open at the same time, thso you can compose or read multiple e-mail messages simultaneously. Similarly, many word processors allow the user to open multiple documents in separate windows, making it possible to switch between them without having to close one to open another. The application in Fig. 22.11 and Fig. 22.12 demonstrates Swing's JDesktopPane and JInternalFrame classes for implementing multiple-document interfaces.
Figure 22.11. Multiple-document interface.
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1 // Fig. 22.11: DesktopFrame.java 2 // Demonstrating JDesktopPane. 3 import java.awt.BorderLayout; 4 import java.awt.Dimension; 5 import java.awt.Graphics; 6 import java.awt.event.ActionListener; 7 import java.awt.event.ActionEvent; 8 import java.util.Random; 9 import javax.swing.JFrame; 10 import javax.swing.JDesktopPane; 11 import javax.swing.JMenuBar; 12 import javax.swing.JMenu; 13 import javax.swing.JMenuItem; 14 import javax.swing.JInternalFrame; 15 import javax.swing.JPanel; 16 import javax.swing.ImageIcon; 17 18 public class DesktopFrame extends JFrame 19 { 20 private JDesktopPane theDesktop; 21 22 // set up GUI 23 public DesktopFrame() 24 { 25 super( "Using a JDesktopPane" ); 26 27 JMenuBar bar = new JMenuBar(); // create menu bar 28 JMenu addMenu = new JMenu( "Add" ); // create Add menu 29 JMenuItem newFrame = new JMenuItem( "Internal Frame" ); 30 31 addMenu.add( newFrame ); // add new frame item to Add menu 32 bar.add( addMenu ); // add Add menu to menu bar 33 setJMenuBar( bar ); // set menu bar for this application 34 35 theDesktop = new JDesktopPane(); // create desktop pane 36 add( theDesktop ); // add desktop pane to frame 37 38 // set up listener for newFrame menu item 39 newFrame.addActionListener( 40 41 new ActionListener() // anonymous inner class 42 { 43 // display new internal window 44 public void actionPerformed( ActionEvent event ) 45 { 46 // create internal frame 47 JInternalFrame frame = new JInternalFrame( 48 "Internal Frame", true, true, true, true ); 49 50 MyJPanel panel = new MyJPanel(); // create new panel 51 frame.add( panel, BorderLayout.CENTER ); // add panel 52 frame.pack(); // set internal frame to size of contents 53 54 theDesktop.add( frame ); // attach internal frame 55 frame.setVisible( true ); // show internal frame 56 } // end method actionPerformed 57 } // end anonymous inner class 58 ); // end call to addActionListener 59 } // end DesktopFrame constructor 60 } // end class DesktopFrame 61 62 // class to display an ImageIcon on a panel 63 class MyJPanel extends JPanel 64 { 65 private static Random generator = new Random(); 66 private ImageIcon picture; // image to be displayed 67 private String[] images = { "yellowflowers.png", "purpleflowers.png", 68 "redflowers.png", "redflowers2.png", "lavenderflowers.png" }; 69 70 // load image 71 public MyJPanel() 72 { 73 int randomNumber = generator.nextInt( 5 ); 74 picture = new ImageIcon( images[ randomNumber ] ); // set icon 75 } // end MyJPanel constructor 76 77 // display imageIcon on panel 78 public void paintComponent( Graphics g ) 79 { 80 super .paintComponent( g ); 81 picture.paintIcon( this, g, 0, 0 ); // display icon 82 } // end method paintComponent 83 84 // return image dimensions 85 public Dimension getPreferredSize() 86 { 87 return new Dimension( picture.getIconWidth(), 88 picture.getIconHeight() ); 89 } // end method getPreferredSize 90 } // end class MyJPanel |
Figure 22.12. Test class for DeskTopFrame.
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1 // Fig. 22.12: DesktopTest.java 2 // Demonstrating JDesktopPane. 3 import javax.swing.JFrame; 4 5 public class DesktopTest 6 { 7 public static void main( String args[] ) 8 { 9 DesktopFrame desktopFrame = new DesktopFrame(); 10 desktopFrame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE ); 11 desktopFrame.setSize( 600, 480 ); // set frame size 12 desktopFrame.setVisible( true ); // display frame 13 } // end main 14 } // end class DesktopTest
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Lines 2733 create a JMenuBar, a JMenu and a JMenuItem, add the JMenuItem to the JMenu, add the JMenu to the JMenuBar and set the JMenuBar for the application window. When the user selects the JMenuItem newFrame, the application creates and displays a new JInternalFrame object containing an image.
Line 35 assigns JDesktopPane (package javax.swing) variable theDesktop a new JDesktopPane object that will be used to manage the JInternalFrame child windows. Line 36 adds the JDesktopPane to the JFrame. By default, the JDesktopPane is added to the center of the content pane's BorderLayout, so the JDesktopPane expands to fill the entire application window.
Lines 3958 register an ActionListener to handle the event when the user selects the newFrame menu item. When the event occurs, method actionPerformed (lines 4456) creates a JInternalFrame object in lines 4748. The JInternalFrame constructor used here takes five argumentsa string for the title bar of the internal window, a boolean indicating whether the internal frame can be resized by the user, a boolean indicating whether the internal frame can be closed by the user, a boolean indicating whether the internal frame can be maximized by the user and a boolean indicating whether the internal frame can be minimized by the user. For each of the boolean arguments, a true value indicates that the operation should be allowed (as is the case here).
As with JFrames and JApplets, a JInternalFrame has a content pane to which GUI components can be attached. Line 50 creates an instance of our class MyJPanel (declared at lines 6390) that is added to the JInternalFrame at line 51.
Line 52 uses JInternalFrame method pack to set the size of the child window. Method pack uses the preferred sizes of the components to determine the window's size. Class MyJPanel declares method getPreferredSize (lines 8589) to specify the panel's preferred size for use by the pack method. Line 54 adds the JInternalFrame to the JDesktopPane, and line 55 displays the JInternalFrame.
Classes JInternalFrame and JDesktopPane provide many methods for managing child windows. See the JInternalFrame and JDesktopPane online API documentation for complete lists of these methods:
java.sun.com/j2se/5.0/docs/api/javax/swing/JInternalFrame.html
java.sun.com/j2se/5.0/docs/api/javax/swing/JDesktopPane.html