请将下列程序的空白处补充完整。
Import java.awt.*;
Public class E11__4
Public static void main(String args[])
Frame f=new Frame("BorderLayout");
_________;
f.add("North",new button("North"));
f.add("East",new button("East"));
f.add("West",new button("West"));
f.add("South",tf);
f.setSize(200,200)
f.pack():
f.setVisible(true);