import java.awt.*;
import java.awt.event.*;
public class E17 extends Frame implements ItemListener
{
      List list;
      TextField tf;
      public E17()
      {
              setSize(400,300);
              setLayout(new FlowLayout());
              list=new List(4);
              list.add("高中");
              list.add("大専");
              list.add("本科");
              list.add("研究生");
              tf=new TextField(10);tf.setEditable(false);
              add(list);
              add(tf);
              list.addItemListener(this);
          this.addWindowListener(new WindowAdapter()
          {
               public void windowClosing(WindowEvent e)
               { System.exit(0); }
          });
    }    public E17(String s)
    {
        this();
        setTitle(s);
    }
    public void itemStateChanged(ItemEvent e)
    {
        String s=null;
        s=((Choice)e.getSource()).getSelectedItem();
        tf.setText(s);
    }
    public static void main(String[]args)
    {
        E17 f=new E17(" Choice Example");
        f.setVisible(true);
    }
}list右边框里不显示选择内容,为什么?