java程序用eclipse无法运行！

import java.awt.event.*;
import acm.graphics.*;

class MyCanvas extends GCanvas implements ComponentListener{
public MyCanvas(){
addComponentListener(this);
rect = new GRect(BW,BH);
rect.setFilled(true);
}

public void update(){
removeAll();
add(rect,(getWidth()-BW)/2,(getHeight()-BH)/2);
}

public void componentResized(ComponentEvent e) {update();}
public void componentMoved(ComponentEvent e) {}
public void componentShown(ComponentEvent e) {}
public void componentHidden(ComponentEvent e) {}

private static final double BW = 50;
private static final double BH = 50;
private GRect rect;
}