import java.awt.Color;
import java.awt.Graphics;
import java.awt.Image; // Used to create an image buffer
import java.awt.Graphics2D; // Used for anti-aliasing
import java.awt.RenderingHints; // Used for anti-aliasing

import java.applet.Applet;

public class GraphicsMoveObjectsWithThreadAndApplet extends Applet implements Runnable
{
	Thread runner = null;
	Image image;
	Graphics graphics;
	int width = 400, height = 250;
	int dotSize = 25, dotBlueX = 150, dotBlueY = 70, dotMagentaX = 230, dotMagentaY = 190;
	int directionBlue = 1, speedBlue = 2, directionMagenta = 1, speedMagenta = 4;

	public void init()
	{
		// Make sure objects can be positioned on the applet window
		//  and set the applet background color, size, and visibility
		setLayout(null);
		setBackground(Color.WHITE);
		setSize(width, height);
		setVisible(true);
	}

	public void start()
	{
		// After the applet is initialized, this method will be called;
		//  a thread is started here that will, through the 'run'
		//  method (below), control the movement of the two dots
		if (runner == null)
		{
			runner = new Thread(this);
			runner.start();
		}
	}

	public void stop()
	{
		// This method will be called when the user leaves the Web page
		//  on which this applet is running (or manually closes the applet
		//  window if the applet is not being run through a Web browser);
		//  The variable 'runner' will be set to 'null' so that the loop
		//  in the 'run' method (below) will end
		runner = null;
	}

	// Since a timer is not being used, this method should be set to
	//  continuously repeat (loop); a thread is used (below) to pause
	//  the loop, which effectively simulates a timer with an interval 
	public void run()
	{
		// This loop condition ensures that the thread will continue to
		//  run only as long as necessary; when the applet is closed,
		//  the 'stop' method is called (above), which will, in turn
		//  (by setting the variable 'runner'), cause this loop to end
		while (runner != null)
		{
			// Update the position/direction of the blue dot 
			dotBlueX += speedBlue * directionBlue;
			if (dotBlueX < 16 || dotBlueX > width - 18)
				directionBlue = -directionBlue;

			// Update the position/direction of the magenta dot
			dotMagentaX += speedMagenta * directionMagenta;
			if (dotMagentaX < 16 || dotMagentaX > width - 18)
				directionMagenta = -directionMagenta;

			repaint();

			try
			{
				// Pause for 15/1000 seconds (so that the dots do not move
				//  across the frame too quickly
				Thread.sleep(15);
			}
			catch (InterruptedException e)
			{
				// This section is required when using 'Thread.sleep()'
			}
		}
	}

	public void paint(Graphics g)
	{
		// Prepare to create the image on a separate 'Image' instance; this
		//  should prevent flickering by using a "buffer" on which the frame
		//  image will first be drawn before it is displayed to the user
		image = createImage(width, height);
		graphics = image.getGraphics();

		// This line causes graphics and text to be rendered with anti-aliasing
		//  turned on, making the overall display look smoother and cleaner
		((Graphics2D) graphics).setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

		// Draw/Redraw the blue dot
		graphics.setColor(Color.BLUE);
		graphics.fillOval(dotBlueX - dotSize / 2, dotBlueY - dotSize / 2, dotSize, dotSize);

		// Draw/Redraw the magenta dot
		graphics.setColor(Color.MAGENTA);
		graphics.fillOval(dotMagentaX - dotSize / 2, dotMagentaY - dotSize / 2, dotSize, dotSize);

		// Display (Draw) the buffered image on the frame
		g.drawImage(image, 0, 0, null);
	}
}