java - Why I have different results from run() method in two classes? -

first :

import acm.graphics.grect; import acm.program.graphicsprogram;  public class graphtest extends graphicsprogram{ public void run(){     grect a= new grect(50, 50);     add(a,50,50); } } 

this show rectangle on screen.

second:

public class myprog extends program{ public void run(){     mycanvas canvas = new mycanvas();     add(canvas); } }  import java.awt.event.*; import acm.graphics.*;  public class mycanvas extends gcanvas implements componentlistener{ private grect rect; private static final double box_width = 50; private static final double box_height= 50; public mycanvas(){     addcomponentlistener(this);     rect = new grect(box_width, box_height);     rect.setfilled(false);     add(rect,10,10); } public void update(){     grect rect2 = new grect(0.1*getwidth(), 0.1*getheight());     add(rect2,(getwidth()-box_width)/2,(getheight()-box_height)/2); } public void componentresized(componentevent e){update();} public void componenthidden(componentevent e){} public void componentmoved(componentevent e){} public void componentshown(componentevent e){} } 

this supposed show me rectangle, doesn't. if use init() 2 rectangles(rectand rect2) shows.

anyone can use example me understanding use of run() , init() , why have different results when i'm using run()?