Learning Java

The PopupMenu Class

One of Swing’s nifty components is JPopupMenu, a menu that automatically appears when you press the appropriate mouse button inside of a component. (On a Windows system, for example, clicking the right mouse button invokes a popup menu.) Which button you press depends on the platform you’re using; fortunately, you don’t have to care—Swing figures it out for you.

The care and feeding of JPopupMenu is basically the same as any other menu. You use a different constructor (JPopupMenu( )) to create it, but otherwise, you build a menu and add elements to it the same way. The big difference is you don’t need to attach it to a JMenuBar. Instead, just pop up the menu whenever you need it.

The following example, PopupColorMenu, contains three buttons. You can use a JPopupMenu to set the color of each button or the frame itself, depending on where you press the mouse. Figure 14.5 shows the example in action; the user is preparing to change the color of the bottom button.

Figure 14-5. The PopupColorMenu application

//file: PopUpColorMenu.java import java.awt.*; import java.awt.event.*; import javax.swing.*; public class PopUpColorMenu extends JFrame implements ActionListener { JPopupMenu colorMenu; Component selectedComponent; public PopUpColorMenu( ) { super("PopUpColorMenu v1.0"); setSize(100, 200); setLocation(200, 200); addWindowListener(new WindowAdapter( ) { public ...