How to write a Component Listener in Java?

[hariharan_00]

Hi friends,
Last time you all guys helped me a lot. So i thought that this is perfect place to post my query. I am getting confused while writing the Component Listener..!! I have tried many different ways but not succeeding in any of them. Please help by telling me how to write a Component Listener in Java.?? Hope that I will get the response sooner.!!

[void]

Since, you don't know much about the Component listener, I thought that explaining you about that would be better than telling you the coding. The Component listener is a listener interface for receiving component events. You can define component as an object having a graphical representation that can be displayed on the screen. The user can also interact with the component. Buttons, checkboxes, and scrollbars of a typical graphical user interface are some of the examples of components.

[CodGuru]

The following are the methods of the ComponentListener Interface :

• componentHidden(ComponentEvent) - This method is called after the listened-to component is hidden.
• componentMoved(ComponentEvent) - This method is called after the listened-to component moves.
• componentResized(ComponentEvent) - When the listened-to component's size changes, this method is called.

The following is the method of the ComponentEvent Class :

• Component getComponent() - This method returns the component that fired the event.

[MindSpace]

The following is the code related to handling component events :

public class ComponentEventDemo ... implements ComponentListener {
    static JFrame frame;
    JLabel label;
    ...
    public ComponentEventDemo() {
        ...
        JPanel panel = new JPanel(new BorderLayout());
        label = new JLabel("Example of Label", JLabel.CENTER);
        label.addComponentListener(this);
        panel.add(label, BorderLayout.CENTER);

        JCheckBox checkbox = new JCheckBox("Label visible", true);
        checkbox.addComponentListener(this);
        panel.add(checkbox, BorderLayout.PAGE_END);
        panel.addComponentListener(this);
        ...
        frame.addComponentListener(this);
    }
    ...
     public void componentHidden(ComponentEvent e) {
        displayMessage(e.getComponent().getClass().getName() + " --- Hidden");
    }

    public void componentMoved(ComponentEvent e) {
        displayMessage(e.getComponent().getClass().getName() + " --- Moved");
    }

    public void componentResized(ComponentEvent e) {
        displayMessage(e.getComponent().getClass().getName() + " --- Resized ");            
    }

    public void componentShown(ComponentEvent e) {
        displayMessage(e.getComponent().getClass().getName() + " --- Shown");

    }

    public static void main(String[] args) {
        ...
        frame = new JFrame("ComponentEventDemo");
        ...
        JComponent newContentPane = new ComponentEventDemo();
        frame.setContentPane(newContentPane);
        ...
    }
}

[kyosang]

The following sample creates the GUI and show it. Just have a look at the example :

private static void createAndShowGUI() {
        frame = new JFrame("TrialComponentEvent");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JComponent newContentPane = new ComponentEventDemo();
        newContentPane.setOpaque(true);
        frame.setContentPane(newContentPane);

        frame.pack();
        frame.setVisible(true);
    }