java - Communicating between two JFrames -

sorry if question has been asked i'm having trouble understanding existing answers , need see related code. (i'm new java)

also sorry if similar code posted - tried doing 2 panels on 1 frame , couldnt working im trying method.

when button blacktrail pressed on frame2, changes color of projectile on frame1 black.

here's code far:

gui form class ( menu buttons etc)

 public class guiform1 extends jframe{  //initialise components private jpanel mainpanel; private jpanel menupanel; private jbutton whitetrail; private jbutton blacktrail; private jbutton redtrail; private jbutton bluetrail; private jbutton greentrail; private jbutton purpletrail; //irrelevant components     public guiform1() {        jframe frame2 = new jframe("projectile motion - menu");     frame2.setcontentpane(mainpanel);     frame2.setdefaultcloseoperation(windowconstants.hide_on_close);     frame2.pack();     frame2.setvisible(true);  }  } 

physics sim class (main , graphics drawing)

public class physicssim extends jcomponent {     public static void main(string[] args) {        //building frame fit correct screen size      jframe frame1 = new jframe("projectile motion - animation");     physicssim sim = new physicssim();     frame1.add(sim);     frame1.setdefaultcloseoperation(windowconstants.exit_on_close);     frame1.setlocationrelativeto(null);     frame1.setvisible(true);     frame1.setextendedstate(frame1.maximized_both);       guiform1 guiform1 = new guiform1();    }    public void paintcomponent(graphics g) {     //background     g.setcolor(new color(149, 179, 215));     g.fillrect(0, 0, getwidth(), getheight());     super.paintcomponent(g);      //axis     g.setcolor(color.black);     g.fillrect(50, 0, 5, getheight());     g.fillrect(0, getheight() - 50, getwidth(), 5);       int axisy = 0;     int axisx = 0;     int axisycounter = 1;     int axisxcounter = 1;      //axis markers     while (axisycounter <= getheight() / 10) {         g.fillrect(35, axisy, 20, 5);         axisy = axisy + 50;         axisycounter++;     }      while (axisxcounter <= getwidth() / 10) {         g.fillrect(axisx, getheight() - 50, 5, 20);         axisx = axisx + 50;         axisxcounter++;     }     //projectile      g.setcolor(c);     g.filloval(getwidth() - 1885, getheight() - 60, 30, 30);     } public color c = color.white;   }