Step 2

In step 2, we add function that allows the user to draw on the drawing panel by holding down the mouse button and dragging. Note: no function has been added for the clear button.

The new function is found in the MyPanel class. Specifically, it implements two java.awt.event interfaces: MouseListener and MouseMotionListener. In the first example, below, only skeleton methods are included. In the second, code is added to perform the drawing function.

Example Applet: Skeleton Version

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

public class Step2 extends Applet {

    //  Add drawing function

    Button clear;
    Panel buttonPanel;
    MyPanel drawPanel;

    public void init() {

        super.init();

        clear = new Button ( "clear" );
        buttonPanel = new Panel ();
        drawPanel = new MyPanel ();

        clear.setBackground ( new Color (187, 00, 00)  );
        clear.setForeground ( Color.white );

        buttonPanel.setBackground ( new Color (00, 102, 155)  );
        buttonPanel.add ( clear );

        drawPanel.setBackground ( Color.white );
        drawPanel.setForeground ( Color.black );

        setLayout ( new BorderLayout () );
        add ( "North", buttonPanel );
        add ( "Center", drawPanel );

        drawPanel.addMouseListener ( drawPanel );
        drawPanel.addMouseMotionListener ( drawPanel );

    }  // end init


}  // end Step2

 

class MyPanel extends Panel implements MouseListener, MouseMotionListener {

   //**********************  Interface Methods

   // MouseListener Methods

    public void mousePressed ( MouseEvent e )  {
    }  // end mousePressed

    public void mouseReleased ( MouseEvent e )  {
    }  // end mouseReleased

    public void mouseEntered ( MouseEvent e )  {
    }  // end mouseEntered

    public void mouseExited ( MouseEvent e )  {
    }  // end mouseExited

    public void mouseClicked ( MouseEvent e )  {
    }  // end mouseClicked

   // MouseMotionListener Methods

    public void mouseDragged ( MouseEvent e )  {
    }  // end mouseDragged

    public void mouseMoved ( MouseEvent e )  {
    }  // end mouseMoved

}  // end MyPanel

---

 

In the example, below, code is added in the MyPanel class to perform the drawing function, using the mouse.

Example Applet

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

public class Step2 extends Applet {

    //  Add drawing function

    Button clear;
    Panel buttonPanel;
    MyPanel drawPanel;


    public void init() {

        super.init();

        clear = new Button ( "clear" );
        buttonPanel = new Panel ();
        drawPanel = new MyPanel ();

        clear.setBackground ( new Color (187, 00, 00)  );
        clear.setForeground ( Color.white );

        buttonPanel.setBackground ( new Color (00, 102, 155)  );
        buttonPanel.add ( clear );

        drawPanel.setBackground ( Color.white );
        drawPanel.setForeground ( Color.black );

        setLayout ( new BorderLayout () );
        add ( "North", buttonPanel );
        add ( "Center", drawPanel );

        drawPanel.addMouseListener ( drawPanel );
        drawPanel.addMouseMotionListener ( drawPanel );

    }  // end init


}  // end Step2

 

class MyPanel extends Panel implements MouseListener, MouseMotionListener {

    private int last_x, last_y, x, y;

   //**********************  Interface Methods

    // MouseListener Methods

    public void mousePressed ( MouseEvent e )  {
        last_x = e.getX();
        last_y = e.getY();
    }  // end mousePressed

    public void mouseReleased ( MouseEvent e )  {
    }  // end mouseReleased

    public void mouseEntered ( MouseEvent e )  {
        requestFocus ();
    }  // end mouseEntered

    public void mouseExited ( MouseEvent e )  {
    }  // end mouseExited

    public void mouseClicked ( MouseEvent e )  {
    }  // end mouseClicked

    // MouseMotionListener Methods

    public void mouseDragged ( MouseEvent e )  {
        Graphics g;
        x = e.getX();
        y = e.getY();
        g = this.getGraphics ();
        g.drawLine ( last_x, last_y, x, y );
        last_x = x;
        last_y = y;
    }  // end mouseDragged

    public void mouseMoved ( MouseEvent e )  {
    }  // end mouseMoved

}  // end MyPanel

Run the applet