import java.awt.*;
import java.awt.event.*;
class WindowChoice extends Frame implements ItemListener,ActionListener
{
Choice choice;
TextField text;
TextArea area;
Button ad,del;
WindowChoice()
{
setLayout(new FlowLayout());
choice=new Choice();
text=new TextField(8);
area=new TextArea(8,25);
choice.add("音乐天地");
choice.add("无数天地");
choice.add("象棋乐园");
choice.add("交友聊天");
ad.addActionListener(this);
del.addActionListener(this);
text.addActionListener(this);
choice.addItemListener(this);
add(choice);
add(del);
add(ad);
add(area);
add(text);
setSize(200,200);
setVisible(true);
validate();
}
public void itemStateChanged(ItemEvent e)
{
String name=choice.getSelectedItem();
int index=choice.getSelectedIndex();
area.setText("\n"+index+":"+name);
}
public void actionPerformed(ActionEvent e)
{
if(e.getSource()==ad||e.getSource()==text)
{
String name=text.getText();
choice.add(name);
choice.select(name);
area.append("\n列表添加"+name);

}
else if(e.getSource()==del)
{
area.append("\n列表删除"+choice.getSelectedItem());
choice.remove(choice.getSelectedIndex());
}
}
}
public class Example6
{
public static void main(String [] args)
{
new WindowChoice();
}
}

出现Exception in thread "main" java.lang.NullPointerException
at WindowChoice.<init>(Example6.java:19)
at Example6.main(Example6.java:59)
刚开始学习java各位高手能指点一下么，感激涕零！！！！

你的两个按钮都没有实例化,ad=new Button("添加");del.....
看你初学,出现这种问题可以原谅,以后细心点.

Exception in thread "main" java.lang.NullPointerException
"说明是引用错误,即你声明了对象但没有创建就使用,会出现异常的"

import java.awt.*;
import java.awt.event.*;
class WindowChoice extends Frame implements ItemListener,ActionListener
{
    Choice choice;
    TextField text;
    TextArea area;
    Button ad,del;
    WindowChoice()
    {
        setLayout(new FlowLayout());
        choice=new Choice();
        text=new TextField(8);
        area=new TextArea(8,25);
        choice.add(\"音乐天地\");
        choice.add(\"无数天地\");
        choice.add(\"象棋乐园\");
        choice.add(\"交友聊天\");
        ad=new Button(\"添加\"); //光声明了没有创佳对象
        del=new Button(\"删除\");
        ad.addActionListener(this);
        del.addActionListener(this);
        text.addActionListener(this);
        choice.addItemListener(this);
        add(choice);
        add(del);
        add(ad);
        add(area);
        add(text);
        setSize(200,200);
        setVisible(true);
        validate();
    }
    public void itemStateChanged(ItemEvent e)
    {
        String name=choice.getSelectedItem();
        int index=choice.getSelectedIndex();
        area.setText(\"\n\"+index+\":\"+name);
    }
    public void actionPerformed(ActionEvent e)
    {
        if(e.getSource()==ad||e.getSource()==text)
        {
            String name=text.getText();
            choice.add(name);
            choice.select(name);
            area.append(\"\n列表添加\"+name);
            
        }
        else if(e.getSource()==del)
        {
            area.append(\"\n列表删除\"+choice.getSelectedItem());
            choice.remove(choice.getSelectedIndex());
        }
    }
}
public class Example6
{
    public static void main(String [] args)
    {
        new WindowChoice();
    }
}

功能也不行.

嗯 应该是"表单"练习的小程序
既然是AWT 最好再加个 窗口监听

addWindowListener( new WindowAdapter()
{ public void windowClosing(WindowEvent e)
{ System.exit(0);
}
}
);
//这样能把关掉窗口