import javax.swing.*;  // For JApplet
import java.awt.*;     // Abstract Windowing Tookit:  graphics stuff 

public class Circles extends JApplet 
{  
     // Draw an unfilled circle colored c centered at (x,y) with radius r 
     // in graphics context g.  Leave the current graphics color invariant.
     public static void drawCircle (Graphics g, Color c, int x, int y, int r) 
     {
          Color savedColor = g.getColor();
          g.setColor(c);
          g.drawOval(x + 1 - r, y + 1 - r, 2*r - 1, 2* r -1); // Be careful of fencepost errors!
          g.setColor(savedColor);
     }
     
     public void paint (Graphics g) 
     {
          Dimension screenSize = getSize(); // Get the applet's size
          int x1 = screenSize.width/4;
          int y1 = screenSize.height/4; 
          int x2 = 3*screenSize.width/4;
          int y2 = 3*screenSize.height/4; 
          
          // Draws concentric red circles centered about (x1,y1)
          for (int i = 1; i <= 128; i = i + 10) {
               drawCircle(g, Color.red, x1, y1, i);
          }
          
          // Draws concentric red circles centered about (x1,y1).
          // These are close enough to exhibit Moire patterns.
          for (int i = 1; i <= 128; i = i + 2) {
               drawCircle(g, Color.red, x2, y1, i);
          }
          
          // Draws concentric red circles centered about (x1,y1).
          // These are close enough to give a solid circle.
          for (int i = 1; i <= 128; i++) {
               drawCircle(g, Color.red, x1, y2, i);
          }
          
          // Draws concentric circles centered about (x1,y1)
          // that vary in shade from red (small circles) to 
          // blue (large circles). 
          for (int i = 1; i <= 128; i++) {
               drawCircle(g, new Color (255 - (2*i - 1), 0, 2*i - 1), x2, y2, i);
          }  
     }  
}