Circle.java

import java.awt.Color; import java.awt.Graphics2D; import java.awt.geom.Ellipse2D; import java.awt.geom.Point2D; /** This class implements a Circle. It includes a method to test whether two circles intersect. */ public class Circle { private double xCenter; private double yCenter; private double radius; private Color color; /** Constructs a black circle. @param x the x-coordinate of the center @param y the y-coordinate of the center @param r the radius */ public Circle(double x, double y, double r) { xCenter = x; yCenter = y; radius = r; color = Color.BLACK; } /** Sets the color of this circle. @param aColor the color */ public void setColor(Color aColor) { color = aColor; } /** Draws the circles. @param g2 the graphics context */ public void draw(Graphics2D g2) { if (radius < 0) return; g2.setColor(color); // draw the circle Ellipse2D.Double circle = new Ellipse2D.Double(xCenter - radius, yCenter - radius, 2 * radius, 2 * radius); g2.draw(circle); } /** Tests whether or not the two circles intersect with each other. @param other the other circle @return true the two circles intersect */ public boolean intersects(Circle other) { . . . } }

CircleComponent.java

import java.awt.Color; import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.geom.Ellipse2D; import java.awt.geom.Point2D; import javax.swing.JComponent; import javax.swing.JPanel; /** Shows two Circles and tests whether they intersect or not. */ public class CircleComponent extends JComponent { private Circle circle1; private Circle circle2; /** Constructs a component for showing two circles. @param r1 the radius of the first circle @param r2 the radius of the second circle */ public CircleComponent(double r1, double r2) { String message; circle1 = new Circle(100, 200, r1); circle2 = new Circle(200, 100, r2); Color color; if (. . .) color = Color.GREEN; else color = Color.RED; circle1.setColor(color); circle2.setColor(color); } public void paintComponent(Graphics g) { Graphics2D g2 = (Graphics2D) g; circle1.draw(g2); circle2.draw(g2); } }

Use the following files:

CircleViewer.java

import javax.swing.JFrame;
import javax.swing.JOptionPane;

/**
   This program views two circles.
*/
public class CircleViewer
{
   public static void main(String[] args)
   {
      JFrame frame = new JFrame();

      final int FRAME_WIDTH = 400;
      final int FRAME_HEIGHT = 400;

      frame.setSize(FRAME_WIDTH, FRAME_HEIGHT);
      frame.setTitle("CircleViewer");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

      String input = JOptionPane.showInputDialog("Radius 1:");
      double r1 = Double.parseDouble(input);

      input = JOptionPane.showInputDialog("Radius 2:");
      double r2 = Double.parseDouble(input);

      CircleComponent component = new CircleComponent(r1, r2);
      frame.add(component);

      frame.setVisible(true);
   }
}

CircleViewerSnap.java

import javax.swing.JFrame;
import javax.swing.JOptionPane;

/**
   This program views two circles.
*/
public class CircleViewerSnap
{
   public static void main(String[] args)
   {
      JFrame frame = new JFrame();

      final int FRAME_WIDTH = 400;
      final int FRAME_HEIGHT = 400;

      frame.setSize(FRAME_WIDTH, FRAME_HEIGHT);
      frame.setTitle("CircleViewer");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

      CircleComponent component = new CircleComponent(60, 85);
      frame.add(component);

      frame.setVisible(true);
   }
}