Something

import java.util.Random;
import java.applet.*;
import java.awt.*;

/*
<applet code="CockroachWalk" width=600 height=600>
</applet>
*/

public class CockroachWalk extends Applet implements Runnable
{
	final int UP = 0, DOWN = 1, LEFT = 2 , RIGHT = 3 , NSTEPS = 5;
	final int STEPSIZE = 30;
	int maxRows , maxCols ;
	int row , col ;
	Thread t = null;
	Image roach , up , down , left , right;
	
	public void init ()
	{
		maxRows = getSize().height;
		maxCols = getSize().width;
		setBackground (Color.white);
		row = maxRows / 2;
		col = maxCols / 2;
		up = getImage (getDocumentBase() , "Roach_Up.jpg");
		down = getImage (getDocumentBase() , "Roach_Down.jpg");
		left = getImage (getDocumentBase() , "Roach_Left.jpg");
		right = getImage (getDocumentBase() , "Roach_Right.jpg");
	}
	
	public void start ()
	{
		if (t == null)
		{
			t = new Thread (this);	
			t.start();
		}
	}
	
	public void run ()
	{
		try
		{
			Random r = new Random ();
			while (true)
			{
				int dir = r.nextInt(4);				//Choose random direction
				loop:
				for (int i = 1 ; i <= NSTEPS; i++)	//Move cockroach along the direction NSTEPS times
				{
					switch (dir)
					{
							case UP:
										if (row <= 0)
										{
											dir = r.nextInt(4);
											continue loop;
										}
										row -= STEPSIZE;
										roach = up;
										break;
							case DOWN:	
										if (row >= maxRows - STEPSIZE)
										{
											dir = r.nextInt(4);
											continue loop;
										}
										row += STEPSIZE;
										roach = down;
										break;
							case LEFT:
										if (col <= 0)
										{
											dir = r.nextInt(4);
											continue loop;
										}
										col -= STEPSIZE;
										roach = left;
										break;
							case RIGHT:
										if (col >= maxCols - STEPSIZE)
										{
											dir = r.nextInt(4);
											continue loop;
										}
										col += STEPSIZE;
										roach = right;
										break;
					}	
					repaint ();
					t.sleep (100);
				}
			}
		}
		catch (InterruptedException e)
		{
			System.out.println("Thread interrupted");
		}
	}
			
	public void paint (Graphics g)
	{
		//DrawCockroach
		g.drawImage (roach , col , row , this );
		
	}
	
}