Java Cookbook

Displaying GUI Components

Problem

You want to create some GUI components and have them appear in a window.

Solution

Create a JFrame and add the components to its ContentPane.

Discussion

The older Abstract Windowing Toolkit (AWT) had a simple frame component that allowed you to add components directly to it. “Good” programs always created a panel to fit inside the frame, and populated that. But some less-educated heathens often added components directly to the frame. The Swing JFrame is more complex; it comes with not one but two containers already constructed inside it. The ContentPane is the main container; you should normally use it as your JFrame’s main container. The GlassPane has a clear background and sits over the top of the ContentPane; its primary use is in temporarily painting something over top of the main ContentPane. Because of this, you need to use the JFrame’s getContentPane( ) method:

import java.awt.*;
import javax.swing.*;

public class ContentPane extends JFrame {
    public ContentPane(  ) {
        Container cp = getContentPane(  );
        // now add Components to "cp"...
    }
}

Then you can add any number of components (including containers) into this existing container, using the Container’s add( ) method:

import java.awt.*; import java.awt.event.*; import javax.swing.*; /** Just a Frame */ public class JFrameDemo extends JFrame { boolean unsavedChanges = false; JButton quitButton; /** Construct the object including its GUI */ public JFrameDemo( ) { super("JFrameDemo"); getContentPane( ...