java - Draw random circles, coloring in red any circle not intersecting another circle -

i have java swing assignment following objectives:

1. when program starts, draws 20 unfilled circles, radius , location of each determined @ random.
2. if perimeter line of circle not intersect other circle, draw outline of circle in red. if intersect @ least 1 other circle, draw in black.
3. add jbutton that, each time pressed, creates new set of circles described above.

i've completed objectives #1 , #3 above, i'm stumped on objective #2.

before present code, let me give understanding of math behind it. there 2 ways circle can not intersect circle:

1. the circles far apart share perimeter point, i.e. distance between centers greater sum of radii (d > r1 + r2). example.
2. one circle inside circle, , perimeters not touch, i.e. distance between centers less difference between radii (d < |r1 - r2|). example.

what i've got far:

1. to compare circles, must specified before drawn, used for-loop store 20 values in arrays center coordinates (int[] x, int[] y) , radius (double[] radius).
2. next, used nested for-loops iterate through array , compare 2 circles, except when circle compared (index j = index k). if circles intersect, g.setcolor(color.red). if not, g.setcolor(color.black).

when execute code, circles without overlap colored red. however, of overlapping circles colored red well. assume non-overlapping at time drawn, intersected thereafter. how fix code account discrepancy in time? (problem area located near bottom, in intersectingcircles class)

import java.awt.borderlayout; import java.awt.event.actionlistener; import java.awt.event.actionevent; import java.awt.color; import java.awt.graphics; import javax.swing.jpanel; import javax.swing.jframe; import javax.swing.jbutton;  public class buttonframe extends jframe  {     private final jbutton resetbutton = new jbutton("reset");      public buttonframe()     {         super("drawing random circles");         setlayout(new borderlayout());          intersectingcircles intersectingcircles = new intersectingcircles();          this.add(intersectingcircles, borderlayout.center);         this.add(resetbutton, borderlayout.south);         this.setdefaultcloseoperation(exit_on_close);         this.setsize(1400, 1400);          buttonhandler handler = new buttonhandler();         resetbutton.addactionlistener(handler);     }      private class buttonhandler implements actionlistener     {                @override         public void actionperformed(actionevent event)         {             reset();         }     }      public static void main(string[] args)     {         buttonframe buttonframe = new buttonframe();         buttonframe.setvisible(true);     }      public void reset()     {         buttonframe buttonframe = new buttonframe();         buttonframe.setvisible(true);     } }  class intersectingcircles extends jpanel {        private static final jbutton resetbutton = new jbutton("reset circles");     private static final jframe frame = new jframe("intersecting circles");      @override     public void paintcomponent(graphics g)     {         super.paintcomponent(g);         this.setbackground(color.white);          int[] x = new int[20];         int[] y = new int[20];         int[] diameter = new int[20];         double[] radius = new double[20];           (int = 0; < 20; i++)         {             int xcoord = (int)(math.random() * 600);             int ycoord = (int)(math.random() * 600);             int circlesize = (int)(math.random() * 550);             x[i] = xcoord;             y[i] = ycoord;             diameter[i] = circlesize;             radius[i] = circlesize / 2.0;         }          (int j = 0; j < 20; j++)         {                (int k = 0; k < 20; k++)             {                    if (k != j)                 {                     if (((math.sqrt((x[k] - x[j]) * (x[k] - x[j]) + (y[k] - y[j])                         * (y[k] - y[j]))) > (radius[j] + radius[k])) ||                         ((math.sqrt((x[k] - x[j]) * (x[k] - x[j]) + (y[k] - y[j])                         * (y[k] - y[j]))) < (math.abs(radius[j] - radius[k]))))                         g.setcolor(color.red);                     else                         g.setcolor(color.black);                  g.drawoval(x[j], y[j], diameter[j], diameter[j]);                 }                 else                     continue;             }         }     } } 

you have logic mistake in if statement inside cycle - can set black color revert red other pair circle. possible solution draft:

  (int j = 0; j < 20; j++)     {            g.setcolor(color.red);  //set non-intersect state         (int k = j + 1; k < 20; k++)  //avoid excessive work         {                    if (intersect test)                   {                     g.setcolor(color.black);                     break; //can stop here                   };             g.drawoval(x[j], y[j], diameter[j], diameter[j]);         } }