Interfaces, GUIs, and Applets

CS 161 - Java

A Bigger Applet

Source: examples/ScribbleApplet.java



/** Adapted from Java in a Nutshell

 **/

 

import java.applet.Applet;

import java.awt.Button;

import java.awt.Dimension;

import java.awt.Graphics;

import java.awt.event.ActionListener;

import java.awt.event.ActionEvent;

import java.awt.event.MouseListener;

import java.awt.event.MouseMotionListener;

import java.awt.event.MouseEvent;

 

public class ScribbleApplet extends Applet

  implements ActionListener, MouseListener, MouseMotionListener {

 

  private int last_x, last_y;

 

  public void init() {

    addMouseListener(this);

    addMouseMotionListener(this);

 

    // Create a clear button

    Button b = new Button("Clear");

 

    // Tell the button which object (this applet) has the

    // actionPerformed() method to call when button is clicked.

    b.addActionListener(this);

    add(b);

  }

 

  /** From ActionListener interface: clear the applet area when

   ** button is pressed

   **/

  public void actionPerformed( ActionEvent e) {

    Graphics g = getGraphics();

    g.setColor(getBackground());

    Dimension d = getSize();

    g.fillRect(0, 0, d.width, d.height);

  }

 

  /** From MouseListener interface: remember where mouse was ehen

   ** mouse button is pressed.

   **/

  public void mousePressed( MouseEvent e) {

    last_x = e.getX();

    last_y = e.getY();

  }

 

  /** From MouseMotionListener interface: determine where mouse is

   ** while button is down; draw a line from last position to this

   ** one, remember where mouse is fo next time.

   **/

  public void mouseDragged(MouseEvent e) {

    Graphics g = getGraphics();

    int x = e.getX();

    int y = e.getY();

    g.drawLine(last_x, last_y, x, y);

    last_x = x;

    last_y = y;

  }

 

  /** Both MouseListener and MouseMotionListener interfaces define

   ** other methods that must be implemented.  These do nothing

   ** implementations satisfy the MouseListener interface

   ** "contract".

   **/

  public void mouseReleased(MouseEvent e) {

  }

  public void mouseClicked(MouseEvent e) {

  }

  public void mouseEntered(MouseEvent e) {

  }

  public void mouseExited(MouseEvent e) {

  }

  /** And this do nothing implementation satisfies the

   ** MouseMotionListener interface "contract".

   **/

  public void mouseMoved(MouseEvent e) {

  }

 

  }

jwd