public void createAndShowGUI() {
      window = new JFrame();       ➊
         //...
      canvas = new JPanel () {     ➋
          //...
          }
      };
    canvas.setBackground(Color.white);
    window.getContentPane().add (canvas, BorderLayout.CENTER);  ➌
    canvas.setPreferredSize(new Dimension(400, 400));
    
    JPanel controls = new JPanel();                             ➍
    
    colorChooser1 = new JButton("Color 1");                     ➎
    controls.add (colorChooser1);
      //...
    colorChooser2 = new JButton("Color 2");
    controls.add (colorChooser2);
      //...
    stepSizeIn = new JTextField (""+stepSize, 5);
    controls.add (stepSizeIn);
      //...
    window.getContentPane().add (controls, BorderLayout.SOUTH);  ➏
      //...
    window.pack();                                               ➐
    window.setVisible(true);
  }

  public void createAndShowGUI() {
      window = new JFrame();
      // set up the components
      window.getContentPane().setLayout (new BorderLayout());
    
      canvas = new JPanel () {
          //...
          }
      };
    canvas.setBackground(Color.white);
    window.getContentPane().add (canvas, BorderLayout.CENTER);
canvas.setPreferredSize(new Dimension(400, 400));  ➊
    
    JPanel controls = new JPanel();
    
    colorChooser1 = new JButton("Color 1");
    controls.add (colorChooser1);
    setColor(colorChooser1, colors[0]);
    colorChooser1.addActionListener (new ColorChooser(colorChooser1, 0));
    
    colorChooser2 = new JButton("Color 2");
    controls.add (colorChooser2);
    setColor(colorChooser2, colors[1]);
    colorChooser2.addActionListener (new ColorChooser(colorChooser2, 1));
    
    stepSizeIn = new JTextField (""+stepSize, 5);
    controls.add (stepSizeIn);
    stepSizeIn.addActionListener (new ActionListener()
      {
        public void actionPerformed(ActionEvent e) {
          try {
            Integer newSize = new Integer(stepSizeIn.getText());
            stepSize = newSize.intValue();
            canvas.repaint();
          } catch (Exception ex) {};
        }
      });

    window.getContentPane().add (controls, BorderLayout.SOUTH);
    
    window.setDefaultCloseOperation((startedInAnApplet) ? JFrame.DISPOSE_ON_CLOSE : JFrame.EXIT_ON_CLOSE);
    
    window.pack();
    window.setVisible(true);
  }

  /**
   * Sets the background color of a button to the indicated color.
   * Changes the foreground to wither black or white, depending on
   * which will give more contrast agasint the new background.
   * 
   * @param button
   * @param color
   */
  private void setColor(JButton button, Color color) {   ➋
    button.setBackground(color);
    int brightness = color.getRed() + color.getGreen() + color.getBlue(); // max of 3*255
    if (brightness > 3*255/2) {
        // This is a fairly bright color. Use black lettering
        button.setForeground (Color.black);
    } else {
        // This is a fairly dark color. Use white lettering
        button.setForeground (Color.white);
    }
}

  private class ColorChooser implements ActionListener {
      private JButton button;          ➊
      private int colorNum;

      public ColorChooser (JButton button, int colorNum) {
          this.button = button;        ➋
          this.colorNum = colorNum;
      }

      @Override
      public void actionPerformed(ActionEvent arg0) {   ➌
          Color chosen = JColorChooser.showDialog(window, "Choose a color", 
                  colors[colorNum]);
          if (chosen != null) {
              colors[colorNum] = chosen;   ➍
              setColor (button, chosen);
              canvas.repaint();
          }
      }
  };

  private class ColorChooser implements ActionListener {
      private JButton button;
      private int colorNum;

      public ColorChooser (JButton button, int colorNum) {
          this.button = button;
          this.colorNum = colorNum;
      }

      @Override
      public void actionPerformed(ActionEvent arg0) {
          Color chosen = JColorChooser.showDialog(window, "Choose a color", colors[colorNum]);
          if (chosen != null) {
              colors[colorNum] = chosen;
              setColor (button, chosen);
              canvas.repaint();
          }
      }
  };


  public void createAndShowGUI() {
      window = new JFrame();
      // set up the components
      window.getContentPane().setLayout (new BorderLayout());
    
      canvas = new JPanel () {
          public void paint (Graphics g) {
              super.paint(g);
              drawLines (g, getSize());
          }
      };
    canvas.setBackground(Color.white);
    window.getContentPane().add (canvas, BorderLayout.CENTER);
    canvas.setPreferredSize(new Dimension(400, 400));
    
    JPanel controls = new JPanel();
    
    colorChooser1 = new JButton("Color 1");
    controls.add (colorChooser1);
    setColor(colorChooser1, colors[0]);
    colorChooser1.addActionListener (new ColorChooser(colorChooser1, 0));
    
    colorChooser2 = new JButton("Color 2");
    controls.add (colorChooser2);
    setColor(colorChooser2, colors[1]);
    colorChooser2.addActionListener (new ColorChooser(colorChooser2, 1));
    
    stepSizeIn = new JTextField (""+stepSize, 5);
    controls.add (stepSizeIn);
    stepSizeIn.addActionListener (new ActionListener()
      {
        public void actionPerformed(ActionEvent e) {
          try {
            Integer newSize = new Integer(stepSizeIn.getText());
            stepSize = newSize.intValue();
            canvas.repaint();
          } catch (Exception ex) {};
        }
      });

    window.getContentPane().add (controls, BorderLayout.SOUTH);
    
    window.setDefaultCloseOperation((startedInAnApplet) ? JFrame.DISPOSE_ON_CLOSE : JFrame.EXIT_ON_CLOSE);
    
    window.pack();
    window.setVisible(true);
  }

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;

import javax.swing.JApplet;
import javax.swing.JButton;
import javax.swing.JColorChooser;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;

/**
 * A simple example of GUI event handling in a Java application.
 * 
 * This can be run as a main program or as an applet.
 * 
 * @author zeil
 *
 */


public class StringArt extends JApplet {

  private boolean startedInAnApplet;
    
// The Model
  private Color[] colors;
  private int stepSize = 5;
  
  // The View & Controls
  private JFrame window;
  private JPanel canvas;
  private JButton colorChooser1;
  private JButton colorChooser2;
  private JTextField stepSizeIn;
  

  private class ColorChooser implements ActionListener {
      private JButton button;
      private int colorNum;

      public ColorChooser (JButton button, int colorNum) {
          this.button = button;
          this.colorNum = colorNum;
      }

      @Override
      public void actionPerformed(ActionEvent arg0) {
          Color chosen = JColorChooser.showDialog(window, "Choose a color", colors[colorNum]);
          if (chosen != null) {
              colors[colorNum] = chosen;
              setColor (button, chosen);
              canvas.repaint();
          }
      }
  };

  public StringArt()
  {
      startedInAnApplet = false;
      window = null;
      colors = new Color[2];
      colors[0] = Color.red;
      colors[1] = Color.blue;
  }
  
  
  public static void main (String[] args)
  {
      StringArt instance = new StringArt();
      instance.createAndShowGUI();  
  }
  
  public void createAndShowGUI() {
      window = new JFrame();
      // set up the components
      window.getContentPane().setLayout (new BorderLayout());
    
      canvas = new JPanel () {
          public void paint (Graphics g) {
              super.paint(g);
              drawLines (g, getSize());
          }
      };
    canvas.setBackground(Color.white);
    window.getContentPane().add (canvas, BorderLayout.CENTER);
    canvas.setPreferredSize(new Dimension(400, 400));
    
    JPanel controls = new JPanel();
    
    colorChooser1 = new JButton("Color 1");
    controls.add (colorChooser1);
    setColor(colorChooser1, colors[0]);
    colorChooser1.addActionListener (new ColorChooser(colorChooser1, 0));
    
    colorChooser2 = new JButton("Color 2");
    controls.add (colorChooser2);
    setColor(colorChooser2, colors[1]);
    colorChooser2.addActionListener (new ColorChooser(colorChooser2, 1));
    
    stepSizeIn = new JTextField (""+stepSize, 5);
    controls.add (stepSizeIn);
    stepSizeIn.addActionListener (new ActionListener()
      {
        public void actionPerformed(ActionEvent e) {
          try {
            Integer newSize = new Integer(stepSizeIn.getText());
            stepSize = newSize.intValue();
            canvas.repaint();
          } catch (Exception ex) {};
        }
      });

    window.getContentPane().add (controls, BorderLayout.SOUTH);
    
    window.setDefaultCloseOperation((startedInAnApplet) ? JFrame.DISPOSE_ON_CLOSE : JFrame.EXIT_ON_CLOSE);
    
    window.pack();
    window.setVisible(true);
  }
  
  /**
   * Sets the background color of a button to the indicated color.
   * Changes the foreground to wither black or white, depending on
   * which will give more contrast agasint the new background.
   * 
   * @param button
   * @param color
   */
  private void setColor(JButton button, Color color) {
    button.setBackground(color);
    int brightness = color.getRed() + color.getGreen() + color.getBlue(); // max of 3*255
    if (brightness > 3*255/2) {
        // This is a fairly bright color. Use black lettering
        button.setForeground (Color.black);
    } else {
        // This is a fairly dark color. Use white lettering
        button.setForeground (Color.white);
    }
}

  // Applet functions
  
  public void init() {
      startedInAnApplet = true;
  }

public void start() {
    if (window == null)
        createAndShowGUI();
  }
  
  public void stop() {
  }
  
  public void destroy() {
  }
  
  
  
  
  int interpolate (int x, int y, int i, int steps)
  {
    return (i * x + (steps-i)*y) / steps;
  }
  
  
  Color interpolate(Color c1, Color c2, int i, int steps)
  {
    return new Color (interpolate(c1.getRed(), c2.getRed(), i, steps),
                      interpolate(c1.getGreen(), c2.getGreen(), i, steps),
                      interpolate(c1.getBlue(), c2.getBlue(), i, steps));
  }
  

  class Point {
    double x;
    double y;
  }

  Point ptOnCircle (int degrees, int radius, Point center) 
  {
    Point p = new Point();
    double theta = Math.toRadians((double)degrees);
    p.x = center.x + (double)radius * Math.cos(theta);
    p.y = center.y + (double)radius * Math.sin(theta);
    return p;
  }

  public void drawLines(Graphics g, Dimension d)
  {
    int dmin = (d.width < d.height) ? d.width : d.height;
    
    if (stepSize < 1)
      stepSize = 1;

    Point center = new Point();
    center.x = (double)d.width/2.0;
    center.y = (double)d.height/2.0;

    for (int i = 0; i < 60; ++i) {
      Point origin = ptOnCircle(6*i, dmin/2, center);
      int j = i + stepSize;
      while (j >= 60)
        j -= 60;
      while (i != j) {
        Point destination = ptOnCircle(6*j, dmin/2, center);
        g.setColor(interpolate(interpolate(colors[0], colors[1], i%30, 30),
                               interpolate(colors[0], colors[1], j, 60),
                               1, 2));
        g.drawLine ((int)origin.x, (int)origin.y,
                    (int)destination.x, (int)destination.y);
        j += stepSize;
        while (j >= 60)
          j -= 60;
      }
    }
  }
  
  
}