新学Java 用Jcerator 抄了老师代码没法执行

import java.awt.*;public class Sb{    public static void main(String[] args){        Frame f=new Frame();        f.setSize(300,300);        f.setLayout(new GridLayout(2,1));        Panel p1=new Panel();        p1.setLayout(new BorderLayout());        Panel p1_1=new Panel();        p1_1.setLayout(new GridLayout(2,1));        Button bn1=new Button("sb1");        Button bn2=new Button("sb2");        Button bn3=new Button("sb3");        Button bn4=new Button("sb4");        p1.add(bn1,BorderLayout.WEST);        p1_1.add(bn3);        p1_1.add(bn4);        p1.add(p1_1,BorderLayout.CENTER);        p1.add(bn2,BorderLayout.EAST);        f.add(p1);        f.pack();            }}