java - Accessing values from within a method -

the goal of program generate random centers circles , find length between centers of circles.
issue in getd1() method of values 0 (before having 50 added, length ends being 0), center1x, center1y, etc.

however in code have omitted centers assigned circles indeed drawn in random locations, know values center coordinates cannot 0.

i did try assigning values center1x, etc. initialized , error "n must positive number" suspect because there no width nor height before jframe created. suggestions appreciated.

public class draw extends jframe {      public class circle extends jpanel {         int center1x;         int center1y;         int center2x;         int center2y;          @override         protected void paintcomponent(graphics g) {             super.paintcomponent(g);             random rand = new random();             center1x=rand.nextint(getwidth()-100);             center1y=rand.nextint(getheight()-100);             center2x=rand.nextint(getwidth()-100);             center2y=rand.nextint(getheight()-100);             //these coordinates of circles         }          public double getd1() {             //distance method has been omitted, functions , not part of issue             double d1 = distance(center1x+50,center1y+50,center2x+50,center2y+50);             return d1;         }     } } 

ps: distance() function has been omitted since not part of issue, uses distance formula.