PaintComponent performs twice

Question

It bothers me, my code runs and runs, but when I go to run it, it seems like I'm looping twice into loops, can someone help me with my logic? Thanks...

package pkgcirc; import java.util.Random; import javax.swing.JFrame; import javax.swing.JPanel; import java.awt.*; /* * Notes: * Draw 20 circles * radius/location (x/y/r) all random * if (circle) is between radii pt (step thru loop) of all values, if its within , * draw it cyan if it overlaps, else black * */ public class Main extends JPanel { int[] radius = new int [3]; int[] xArray = new int [3]; int[] yArray = new int [3]; public Main() { Random g = new Random(); setPreferredSize (new Dimension(300, 200)); for(int i = 0; i < radius.length; i++) { radius[i] = g.nextInt(50)+1; xArray[i] = g.nextInt(250)+1; yArray[i] = g.nextInt(150)+1; } } public void paintComponent(Graphics page) { super.paintComponent(page); for(int i = 0; i < radius.length; i++) { for (int j = 0; j < radius.length; j++) { int xpoint1 = xArray[i]+radius[i]; int ypoint1 = yArray[i]+radius[i]; int xpoint2 = xArray[j]+radius[j]; int ypoint2 = yArray[j]+radius[j]; int radius1 = radius[i]; int radius2 = radius[j]; boolean Collide = circlesCollide(xpoint1, ypoint1, radius1, radius2, xpoint2, ypoint2); if (i != j && Collide == false) { page.setColor(Color.cyan); page.fillOval(xArray[i] ,yArray[i], radius[i], radius[i]); System.out.println("false"); } else{ System.out.println("true"); page.setColor(Color.black); page.drawOval(xArray[j] ,yArray[j], radius[j], radius[j]); } } System.out.println("BREAK"); } } public boolean circlesCollide(double x1, double y1, double r1, double x2, double y2, double r2){ return (distance(x1, y1, x2, y2) <= (r1 + r2)); } public double distance(double x1, double y1, double x2, double y2) { return Math.sqrt(((x2 - x1) * (x2 - x1)) + ((y2 - y1) * (y2 - y1))); } public static void main (String[] args) { JFrame frame = new JFrame ("Circles"); frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE); frame.getContentPane().add (new Main()); frame.pack(); frame.setVisible(true); } } 

Answer 1

Calling setPreferredSize() and pack() will cause paintComponent() to be called twice, because the mapping needs to be redrawn for each call.

Try removing pack() and move the given size to the bottom, for example:

 public Main() { Random g = new Random(); //setPreferredSize(...); // commented this line for (int i = 0; i < radius.length; i++) { radius[i] = g.nextInt(50) + 1; xArray[i] = g.nextInt(250) + 1; yArray[i] = g.nextInt(150) + 1; } } public void paintComponent(Graphics page) { ... } public static void main(String[] args) { JFrame frame = new JFrame("Circles"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setSize(300, 200); // added this line frame.getContentPane().add(new Main()); // frame.pack(); // commented this line frame.setVisible(true); } 

This should now work correctly.

Answer 2

  for(int i = 0; i < radius.length; i++) { for (int j = 0; j < radius.length; j++) { 

Most loops where you want to compare each pairing of two elements together are written as follows:

  for(int i = 0; i < radius.length; i++) { for (int j = i; j < radius.length; j++) { 

(Note j = i in the second loop.)

It also allows you to remove the test i != j :)

EDIT : Oops; j = i means that you still need i != j test - if you used j = i+1 , you can delete the test i != j . Sigh.:)