Tutorials : Java by Example : Section 6 :
Section Six Contents
Using Mousemove and Mousedrag
Keyboard Commands and Playing Sound
Detecting Collisions and Intersections
A Bouncing Balls Applet

Input Devices

Keyboard Commands and Playing Sound

Most applets rely on mouse input, but sometimes you neeed keyboard input as well. How this is accomplished shows the next applet. You have to klick inside the applet first, to enable keyboard input. Pressing the arrow keys (cursor keys) makes the corresponding triangles turn from red to yellow. Here are some other key constants: F1..F12, HOME, END, PGDN, PGUP. See the documentation for the Event class. Pressing the "S"-key playes a sound file. Sound files for Java applets have to be in the au-format. Since loading a soundfile might go wrong, we have to use the try{} / catch{} statement, to catch exceptions.

//Sourcecode 

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

public class Project30 extends Applet
{
   Image Buffer;
   Graphics gBuffer;
   boolean pressedLeft, pressedRight, pressedUp, pressedDown;
   AudioClip mySound;

   public void init()
   {
      Buffer=createImage(size().width,size().height);
      gBuffer=Buffer.getGraphics();

      try
      {
           mySound=getAudioClip(getCodeBase(),"sound.au");
      }

      catch (Exception e){}
   }

   public boolean keyDown(Event e, int key)
   {
      if(key==Event.LEFT)
      pressedLeft=true;

      if(key==Event.RIGHT)
      pressedRight=true;

      if(key==Event.UP)
      pressedUp=true;
      if(key==Event.DOWN)
      pressedDown=true;

      if(key=='s'||key=='S')
           mySound.play();

      repaint();

      return true;
   }

   public boolean keyUp(Event e, int key)
   {
      pressedLeft=pressedRight=pressedUp=pressedDown=false;

      repaint();

      return true;
   }

   public void drawStuff()
   {
      gBuffer.setColor(Color.blue);
      gBuffer.fillRect(0,0,size().width,size().height);

      gBuffer.setFont(new Font("Helvetica",Font.PLAIN,14));
      gBuffer.setColor(Color.orange);
      //if we want to use "" inside a string, we have to mask it with \!
      gBuffer.drawString ("Click inside the applet, then try",50,30);
      gBuffer.drawString ("the cursor keys and the \"S\"-key!",45,50);

      //left
      int xl[] = {40,100,100};
      int yl[] = {160,130,190};

      if(pressedLeft)
          gBuffer.setColor(Color.yellow);
      else
          gBuffer.setColor(Color.red);

      gBuffer.fillPolygon(xl,yl,3);

      //right
      int xr[] = {260,200,200};
      int yr[] = {160,130,190};

      if(pressedRight)
          gBuffer.setColor(Color.yellow);
      else
          gBuffer.setColor(Color.red);

      gBuffer.fillPolygon(xr,yr,3);

      //up
          int xu[] = {120,150,180};
          int yu[] = {110,60,110};

      if(pressedUp)
          gBuffer.setColor(Color.yellow);
      else
          gBuffer.setColor(Color.red);

      gBuffer.fillPolygon(xu,yu,3);

      //down
      int xd[] = {120,150,180};
      int yd[] = {210,260,210};

      if(pressedDown)
          gBuffer.setColor(Color.yellow);
      else
          gBuffer.setColor(Color.red);

      gBuffer.fillPolygon(xd,yd,3);
   }

   public void update(Graphics g)
   {
      paint(g);
   }

   public void paint(Graphics g)
   {
      drawStuff();
      g.drawImage (Buffer,0,0, this);
   }
}

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