import java.awt.*;
import javax.swing.*;

class Draw extends Canvas{


  int x,y;
  Image bg;
  Graphics d;

  Draw(){
   x=300;y=300;
   d = bg.getGraphics();//ここで発生している
   bg = createImage(x,y);
   }

   public void paint(Graphics g){
    d.clearRect(0,0,x,y);
    d.fillRect(0,0,x,y);
    g.drawImage(bg,0,0,this);
  }
  public void update(Graphics g){paint(g);}