orderlyintersection.java

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import java.applet.Applet;
import java.awt.*;
public class OrderlyIntersection extends Applet implements Runnable
{
	Thread	AnimThread = null;
	ICar LRcar;
	ICar TBcar;
	TrafficCop tCop;
	public void init()
	{
		resize(400,400);
		tCop = new TrafficCop();
		LRcar = new ICar( tCop, ICar.leftToRight, 16 );
		TBcar = new ICar( tCop, ICar.topToBottom, 17 );
	}
	public void start()
	{
		if(AnimThread == null)
		{
			AnimThread = new Thread(this);
			AnimThread.start();
			if( LRcar != null && TBcar != null )
			{
				LRcar.start();
				TBcar.start();
			}
		}
		else
		{
			AnimThread.resume();
			if( LRcar != null )
				LRcar.resume();
			if( TBcar != null )
				TBcar.resume();
		}
	}
	public void stop()
	{
		AnimThread.suspend();
		if( LRcar != null )
			LRcar.suspend();
		if( TBcar != null )
		TBcar.suspend();
	}
	public void run()
	{
		while (true)
		{
			try
			{
				Thread.sleep(50);
			}
			catch (InterruptedException e)
			{
			}
			repaint();
		}
	}
	public void paint(Graphics g)
	{
		Color saveColor = g.getColor();
		g.setColor( Color.black );
		g.fillRect( 0, 180, 400, 40 );
		g.fillRect( 180, 0, 40, 400 );
		LRcar.drawCar( g );
		TBcar.drawCar( g );
	}
	public void update(Graphics g)
	{
		if( !isValid() )
		{
			paint( g );
			return;
		}
		LRcar.updateCar( g );
		TBcar.updateCar( g );
    }
}
class ICar extends Thread
{
	public int lastPos = -1;
	public int carPos = 0;
	public int speed = 10;
	public int direction = 1;
	public TrafficCop tCop;
	public final static int leftToRight = 1;
	public final static int topToBottom = 2;
	public ICar( TrafficCop tCop )
	{
		this( tCop, ICar.leftToRight, 10 );
	}
	public ICar( TrafficCop tCop, int direction, int speed )
	{
		this.tCop = tCop;
		this.speed = speed;
		this.direction = direction;
	}
	public void run()
	{
		while( true )
		{
			tCop.checkAndGo( carPos, speed );
			carPos += speed;
			if( carPos >= 400 )
			{
				carPos = 0;
			}
			try
			{
				Thread.sleep(100);
			}
			catch (InterruptedException e)
			{
			}
		}
	}
	public void drawCar( Graphics g )
	{
		if( direction == ICar.leftToRight )
		{
			if( lastPos >= 0 )
			{
				g.setColor( Color.black );
				g.fillRect( 0+lastPos, 185, 40, 32 );
			}
			g.setColor( Color.gray );
			g.fillOval( 2+carPos, 185, 10, 10 );
			g.fillOval( 26+carPos, 185, 10, 10 );
			g.fillOval( 2+carPos, 205, 10, 10 );
			g.fillOval( 26+carPos, 205, 10, 10 );
			g.setColor( Color.green );
			g.fillRect( 0+carPos, 190, 40, 20 );
			lastPos = carPos;
		}
		else
		{
			if( lastPos >= 0 )
			{
				g.setColor( Color.black );
				g.fillRect( 185, 0+lastPos, 32, 40 );
			}
			g.setColor( Color.gray );
			g.fillOval( 185, 2+carPos, 10, 10 );
			g.fillOval( 185, 26+carPos, 10, 10 );
			g.fillOval( 205, 2+carPos, 10, 10 );
			g.fillOval( 205, 26+carPos, 10, 10 );
			g.setColor( Color.blue );
			g.fillRect( 190, 0+carPos, 20, 40 );
			lastPos = carPos;
		}
	}
	public void updateCar( Graphics g )
	{
		if( lastPos != carPos )
		{
			drawCar(g);
		}
	}
}
class TrafficCop
{
	private	boolean	IntersectionBusy = false;
	public synchronized void checkAndGo( int carPos, int speed )
	{
		if( carPos+40 < 180 && carPos+40+speed >= 180 && carPos+speed <= 220 )
		{
			while( IntersectionBusy )
			{
				try
				{
					wait();
				}
				catch ( InterruptedException e )
				{
				}
			}
			IntersectionBusy = true;
		}
		if( carPos+speed > 220 )
		{
			IntersectionBusy = false;
		}
		notify();
	}
}