JAVA-MANI.BLOGSPOT.COM

To rotate things, we need to convert polar to cartesian coordinates:
x = r * Math.cos(theta); and y = r * Math.sin(theta);
Polar coordinates (r, theta) are just another way of specifying points in a 2D plane, where r represents the distance of a point from the center and theta the angle from the horizontal axis (x-axis) through the center. The following applet shows this principle in a minimized form, it rotates a hand around the center and displays the angle accordingly.


//Sourcecode

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

public class Project40 extends Applet implements Runnable
{
   Thread runner;
   Image Buffer;
   Graphics gBuffer;
   int angle;

   public void init()
   {
       //create graphics buffer, the size of the applet
       Buffer=createImage(size().width,size().height);
       gBuffer=Buffer.getGraphics();
   }

   public void start()
   {
       if (runner == null)
       {
           runner = new Thread (this);
           runner.start();
       }
   }

   public void stop()
   {
       if (runner != null)
       {
           runner.stop();
           runner = null;
       }
   }

   public void run()
   {
       while(true)
       {
           try {runner.sleep(250);}
           catch (Exception e) { }

           repaint();
       }
   }

   void drawStuff()
   {
       //paint background black
       gBuffer.setColor(Color.black);
       gBuffer.fillRect(0,0,size().width,size().height);

       //get the center of the applet
       Point p=new Point(size().width/2, size().height/2);
       //define the hand length
       int LENGTH=70;

       //calculate the vector, using the constant Pi
       double vector = angle * Math.PI*2 / 360.0;

       int vx=(int)(p.x+LENGTH*Math.sin(vector));
       int vy=(int)(p.y-LENGTH*Math.cos(vector));

       gBuffer.setColor(Color.yellow);
       //the hand
       gBuffer.drawLine(p.x, p.y, vx, vy);
       //the round "axis"
       gBuffer.drawOval(p.x-6,p.y-6,12,12);

       //display the angle in degrees
       gBuffer.setFont(new Font("Helvetica",Font.PLAIN,13));
       gBuffer.drawString("Angle="+angle+"°",10,20);

       //increase the angle, to move the hand
       if(angle<360)
           angle++;
       else
           angle=0;
   }

   public void update(Graphics g)
   {
       paint(g);
   }

   public void paint(Graphics g)
   {
       drawStuff();
       g.drawImage (Buffer,0,0, this);
   }
}