import java.awt.*;

public class Piston extends java.applet.Applet 
   implements Runnable{ 
   Image pvtpics[] = new Image[14];
   Image currentimg;
   Thread runner;
   int xpos = 125;
   int ypos=50;
   int i=0;
   MediaTracker tracker;
   Font f=new Font("TimesRoman",Font.BOLD,36);
 
   public void init() {
       String pvtsrc[] = {"tut4f1.gif", "tut4f2.gif", "tut4f3.gif", 
       "tut4f4.gif", "tut4f5.gif", "tut4f6.gif",
       "tut4f7.gif", "tut4f8.gif", "tut4f9.gif", "tut4f10.gif",
       "tut4f11.gif", "tut4f12.gif", "tut4f13.gif", "tut4f14.gif"};
	tracker=new MediaTracker(this);
       for (int i=0; i<pvtpics.length;i++) {
          pvtpics[i]=getImage(getCodeBase(),pvtsrc[i]);
          tracker.addImage(pvtpics[i],0);
       }
        add(new Button("add heat"));
        add(new Button("remove heat"));
  }
  public void start() {
      if (runner == null) {
      runner = new Thread(this);
      runner.start();
      }
   }
    public void stop() {
      if (runner != null) {
      runner.stop();
      runner = null;
      }
}
       public void run() {
       setBackground(Color.white);
       repaint();
       try{tracker.waitForAll();}
       catch(InterruptedException e) {
       return;}
       i=6;
       currentimg=pvtpics[i];
       repaint();
       }
       public boolean action(Event evt, Object arg){
            if(evt.target instanceof Button){
            doButton((String)arg);
            return true;
           } else return false;
        }

        void doButton(String bname){
        if(bname.equals("add heat")) {
        i=i+1;
        if(i>13) i=13;
        currentimg=pvtpics[i];}
        if(bname.equals("remove heat")){
        i=i-1;
        if(i<0) i=0;
        currentimg=pvtpics[i];}
        repaint();
        }
      public void paint(Graphics g) {
      if (tracker.checkID(0))
      /*if (currentimg != null)*/ {
      g.drawImage(currentimg, xpos, ypos, this);
       }
      else{
      g.setFont(f);
      g.setColor(Color.red);
      g.drawString("Loading images",125,80);
      }
    }
}