Draw series of concentric circles with random settings

Question

I'm really stuck on how to go about programming this. Need to draw a series of 8 concentric circles using Java drawArc method with following conditions

using import java.util.Random library

1. Provide for starting the drawings at random location (i.e., the x-y cooridinate must be calculated randomly).
2. Provide a random color for each circle
3. Provide a random diameter for each circle

My current code is able to get random random color for each circle but not clear how to meet other random conditions

// Exercise 12.6 Solution: CirclesJPanel.java
// This program draws concentric circles
import java.awt.Graphics;
import javax.swing.JPanel;

public class ConcentricCircles extends JPanel
{
  // draw eight Circles separated by 10 pixels
   public void paintComponent( Graphics g )
   {
      Random random = new Random();
      super.paintComponent( g );

      // create 8 concentric circles
      for ( int topLeft = 0; topLeft < 80; topLeft += 10 )
      {
         int radius = 160 - ( topLeft * 2 );
         int r = random.nextInt(255);
         int gr = random.nextInt(255);
         int b = random.nextInt(255);
         Color c = new Color(r,gr,b);
         g.setColor(c);
         g.drawArc( topLeft + 10, topLeft + 25, radius, radius, 0, 360 );
      } // end for
   }  
}

// This program draws concentric circles
import javax.swing.JFrame;

public class ConcentricCirclesTest extends JFrame {
    /**
    * @param args
    */
    public static void main(String[] args) {
        // TODO Auto-generated method stub

        JFrame frame=new JFrame("Concentric Circles");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        ConcentricCircles cCirclesJPanel = new ConcentricCircles();
        frame.add(cCirclesJPanel);
        frame.setSize(200,250);
        frame.setVisible(true);


    }//end main
}

Answer 1

Several points are key to such an exercise:

• Start with constants for the number of circles and step size; the random number generator in particular only needs to be created once.

  private static final int N = 8;
  private static final int S = 32;
  private static Random random = new Random();
  

• Choose a random point whose coordinates fall within the drawing area.

  // a random point inset by S
  int x = random.nextInt(getWidth() - S * 2) + S;
  int y = random.nextInt(getHeight() - S * 2) + S;
  

• For each circle, find the diameter as a function of S, adding a random fraction of a step, and render the arc at the chosen point offset by the radius.

  for (int i = 0; i < N; i++) {
      g2d.setColor(…);
      int d = (i + 1) * S + random.nextInt(S / 2);
      int r = d / 2;
      g2d.drawArc(x - r, y - r, d, d, 0, 360);
  }
  

• Resize the enclosing frame, which forces a repaint(), to see the effect.

• As random colors are not always appealing, consider Collections.shuffle() on a List<Color>.

  private final List<Color> clut = new ArrayList<Color>();
  …
  for (int i = 0; i < N; i++) {
      clut.add(Color.getHSBColor((float) i / N, 1, 1));
  }
  …
  Collections.shuffle(clut);
  …
  g2d.setColor(clut.get(i));
  

• Override getPreferredSize() to establsh the drawing panel's size.

  private static final int W = S * 12;
  private static final int H = W;
  …
  @Override
  public Dimension getPreferredSize() {
      return new Dimension(W, H);
  

• See also Initial Threads.