<APPLET CODE="Animazione_0.class" WIDTH="200" HEIGHT="200">...</APPLET>

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

public class Animazione_0 extends Applet
{
   final int ms=100;
   Timer t;

   final int nFrame=12;
   int frame;
   Image iFrame[];

   public void init()
   {
      addMouseListener(new MA());

      iFrame=new Image[nFrame];
      for(int i=0; i<nFrame; i++)
         iFrame[i]=getImage(getCodeBase(), "PT_anim"+i+".gif");
      frame=0;
   }

   public void paint(Graphics g)
   {
      g.drawImage(iFrame[frame], 0, 0, this);
   }

   class MA extends MouseAdapter
   {
      public void mousePressed(MouseEvent me)
      {
         frame++;
         if(frame==nFrame)
            frame=0;
         repaint();
      }
   }
}

1. getImage(), drawImage()

2. addMouseListener(), MouseAdapter, mousePressed()