posted                   

code:

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import java.awt.*;

class Ant extends Frame {

   private int[][] theMap;
   private int mapEdge;

   // 0 is north, 1 is east, 2 is south, 3 is west.
   private int antDirection;

   // Current position.
   private int antXpos;
   private int antYpos;

   // Direction-change table. -1 indicates left, 1 indicates right.
   private static final int[] dirChange = {-1, 1};

   public static void main (String[] args) {
      Ant n = new Ant();
   }

   public Ant() {

      // Setup graphics logistics
      super();
      setUndecorated(true);
      mapEdge = 700;
      setSize(mapEdge, mapEdge);
      setResizable(false);

      // Initialise ant
      antXpos = 50;
      antYpos = 50;
      antDirection = 0;
      theMap = new int[mapEdge][mapEdge];

      show();


      // Main decision loop, run until ant goes off the edge
      while ((antXpos >= 0) && (antXpos < mapEdge) &&
	     (antYpos >= 0) && (antYpos < mapEdge)) {
	 
	 // Change directions
	 antDirection += dirChange[theMap[antXpos][antYpos]];
	 if (antDirection > 3) antDirection = 0;
	 else if (antDirection < 0) antDirection = 3;

	 // Change colour and show new grid
	 theMap[antXpos][antYpos]++;
	 if (theMap[antXpos][antYpos] >= dirChange.length) theMap[antXpos][antYpos] = 0;
	 paint(getGraphics());

	 switch (antDirection) {
	 case 0 : antYpos--;	    // North   
	    break;
	 case 1 : antXpos++;	    // East
	    break;
	 case 2 : antYpos++;	    //South
	    break;
	 case 3 : antXpos--;  	    // West
	    break;
	    // Default should never happen, treat it as north. 
	 default : 
	    antYpos--;
	    antDirection = 0;
	    break;
	 }

	 try {
	    Thread.sleep(25);
	 }
	 catch (InterruptedException e) {}
      }


      System.exit(0);
   }

   public void paint(Graphics g) {
      switch (theMap[antXpos][antYpos]) {
      case 0 :
	 g.setColor(Color.white);
	 break;
      case 1 :
	 g.setColor(Color.black);
	 break;
      default :
	 g.setColor(Color.green);
	 break;
      }
      g.fillRect(2*antXpos, 2*antYpos, 2, 2);
   }
}

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