Source

import java.applet.*;
import java.awt.*;
import java.awt.event.*;

public class AnAppletWithMouseEvents extends Applet implements MouseListener {
    public void init() {
        addMouseListener(this);
		}

    public void mouseClicked(MouseEvent e) {
        String clickDesc;
        if (e.getClickCount() == 2)
            clickDesc = "double";
        else
            clickDesc = "single";

        System.out.println("Mouse was " + clickDesc + "-clicked at location (" +
            e.getX() + ", " + e.getY() + ")");
    }
    public void mouseEntered(MouseEvent e) {}
    public void mouseExited(MouseEvent e) {}
    public void mousePressed(MouseEvent e) {}
    public void mouseReleased(MouseEvent e) {}
}

Notes

• The basic event-handling idea should be familiar by now: register as a listener, handle the event when it occurs, using information obtained from the corresponding Event object
• There are some differences to note however:
  • In the past, we placed a component on the applet and registered with that component as a listener for its events. With the mouse, we similarly register with the object upon which the mouse will be clicked-- in this case the applet itself. Note therefore the absence of a receiver in the registration method invocation (which is equivalenet to the applet invoking one of its own methods):

            addMouseListener(this);			// same as this.addMouseListener(this);
    			

  • The MouseEvent/Listener only handles mouse button events (pressing and releasing the button), and the mouse entering and exiting the component's real estate.
    • For purposes of performance, the more expensive events of mouse motion (which occur with much more frequency) are handled via a separate MouseMotionEvent/Listener, which we deal with in the next section.
  • The MouseListener is the first interface we have encountered that contains more than one method to implement. As we are only interested in the click event (i.e., the mouse is pressed and then released, that will be the only method we will actually provide a body for. All the other methods of the MouseListener interface (mouseEntered, mousePressed, ...) must be included as well, but we will simply provide them with empty bodies. (If you are interested, check out the MouseAdapter class and the notion of the event adapter class in general).

This Applet's Behavior

• The init Method
  • simply tregisters with the applet to listen for mouse events within the applet's real estate
• The mouseClicked method
  • determines whether the event was a single- or double- click using the MouseEvent's getClickCount method
  • determines the mouse's location at the time of the click using the getX, getY methods of the MouseEvent object
  • Prints out this obtained information

Things to Do

• The MouseAdapter class
  • What package is it in?