2. Swing Containers

2. Swing Containers
	Chapter 10. Graphic User Interface

2.1. JFrames

The JFrame class provides windows for applets and applications. GUI based applications generally uses at least one frame.

2.1.1. Code Example

public class FrameWindow extends JFrame {
    boolean inAnApplet;
    JTextArea output;

    public FrameWindow() {
        // Calls the Frame constructor and adds components to the window
        addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                if (inAnApplet)
                    dispose();
                else System.exit(0);
            }
        });
    }

    . . .

    public static void main(String args[]) {
        FrameWindow window = new FrameWindow();
        window.inAnApplet = false;
        window.setTitle("FrameWindow Application");
        window.setSize(450, 200);
        window.setVisible(true);
    }
}

2.1.2. Other methods provided by `JFrame`

String getTitle() and void setTitle(String)
Returns or sets (respectively) the title of the frame's window.
Image getIconImage() and void setIconImage(Image)
Returns or sets (respectively) the image displayed when the window is iconified.
JMenuBar getJMenuBar() and void setJMenuBar(JMenuBar)
Returns or sets (respectively) the menu bar for this frame.

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The JPanel class is a general-purpose Container subclass. You can use it as-is to hold components, or you can define a subclass to perform special functionality, such as event handling for the objects the JPanel contains.

	Note
	The `JApplet` class is a `JPanel` subclass with special hooks to run in a browser or in other applet viewer.

2.2.1. Code Example

JPanel p = new JPanel();
p.add(new JButton("Button 1"));
p.add(new JButton("Button 2"));
p.add(new JButton("Button 3"));

A JPanel subclass that draws a frame border around its contents.

Figure 10.6. JPanel subclass.

class FramedArea extends JPanel {
    public FramedArea() {
        . . .
        // Set the layout manager.
        // Add any components to this panel.
    }

    // Ensure that no component is placed on top of the frame.
    // The inset values were determined by trial and error.
    public Insets getInsets() {
        return new Insets(4, 4, 5, 5);
    }

    //Draw the frame at this Panel's edges.
    public void paint(Graphics g) {
        Dimension d = getSize();
        Color bg = getBackground();
        g.setColor(bg);
        g.draw3DRect(0, 0, d.width - 1, d.height - 1, true);
        g.draw3DRect(3, 3, d.width - 7, d.height - 7, false);
    }
}

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2.3. Dialogs

Swing provides support for custom dialogs with the JDialog class. It also provides a useful class, JOptionPane, that enables the creation of a variety of standard dialogs through its class methods.

Figure 10.7. Dialog

2.3.1. Code Example

class SimpleDialog extends JDialog implements ActionListener {
    JFrame parent;
    JTextField field;
    JButton setButton;

    SimpleDialog(JFrame parent, String title) {
        super(parent, title, false);
        ...
        // Create and add components, such as the set button.   
        // Initialize this dialog to its preferred size.
        pack();
    }

    public void actionPerformed(ActionEvent event) {
        Object source = event.getSource();
        if (source == setButton)
            parent.setTitle(field.getText());
    }
}
     
// Here's the code that brings up the dialog:
SimpleDialog dialog = new SimpleDialog(this, "A Simple Dialog");
dialog.setVisible(true);

2.3.2. JOptionPane

The JOptionPane class displays standard dialogs that prompts the user for input or shows messages. Some of it's main methods are:

Method Name	Description
`showConfirmDialog`	Asks a confirming question, showing the buttons yes,no or cancel.
`showInputDialog`	Prompt the user for some input.
`showMessageDialog`	Tells the user about something.
`showOptionDialog`	The unification of the above three.

The example below cretes a dialog that promps user to choose an option in a list.

Object[] options = { "Option 0", "Option 1", "Option 2", "Option 3" };
JOptionPane.showInputDialog(this, "Message", "Title", JOptionPane.QUESTION_MESSAGE,
                            null, options, options[2]);

Figure 10.8. A JOptionPane input dialog