java - "no conversation" error and stopping the program in android -

please see following code. analysed following code , not seem have wrong in coding. when run following code in emulator, no conversation error.

draw.java

public class draw extends view {     paint paint;      public draw(context context) {         super(context);         paint = new paint(paint.anti_alias_flag);     }      @override     protected  void ondraw(canvas canvas) {         paint.setcolor(color.green);         canvas.drawrect(50,30,100,120,paint);         super.ondraw(canvas);     }} 

mainactivity.java

class mainactivity extends activity {     draw draw;     relativelayout relativelayout;     @override     public void oncreate(bundle s){         super.oncreate(s);         relativelayout = new relativelayout(this);   draw = new draw(this);   relativelayout.addview(draw,240,320);         setcontentview(relativelayout);     } } 

install android studio again. code work well.