java 按键的ActionEvent问题

Question

import javax.swing.*;
import java.awt.event.*;
public class SimpleGuilB implements ActionListener{
JButton button;
public static void main (String[] args){
SimpleGuilB gui=new SimpleGuilB();
gui.go();
}
public void go(){
JFrame frame=new JFrame();
JButton button=new JButton("click me");

button.addActionListener(this);

frame.getContentPane().add(button);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(300,300);
frame.setVisible(true);
}
public void actionPerformed(ActionEvent event){
button.setText("I've been click");
}
}代码如上，生成界面后点击按钮后报错，
Microsoft Windows XP [版本 5.1.2600]
(C) 版权所有 1985-2001 Microsoft Corp.C:\Documents and Settings\Administrator>java SimpleGuilB
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at SimpleGuilB.actionPerformed(SimpleGuilB.java:21)
        at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
        at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
        at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
        at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
        at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Sour
ce)
        at java.awt.Component.processMouseEvent(Unknown Source)
        at javax.swing.JComponent.processMouseEvent(Unknown Source)
        at java.awt.Component.processEvent(Unknown Source)
        at java.awt.Container.processEvent(Unknown Source)
        at java.awt.Component.dispatchEventImpl(Unknown Source)
        at java.awt.Container.dispatchEventImpl(Unknown Source)
        at java.awt.Component.dispatchEvent(Unknown Source)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
        at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
        at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
        at java.awt.Container.dispatchEventImpl(Unknown Source)
        at java.awt.Window.dispatchEventImpl(Unknown Source)
        at java.awt.Component.dispatchEvent(Unknown Source)
        at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
        at java.awt.EventQueue.access$200(Unknown Source)
        at java.awt.EventQueue$3.run(Unknown Source)
        at java.awt.EventQueue$3.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Sour
ce)
        at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Sour
ce)
        at java.awt.EventQueue$4.run(Unknown Source)
        at java.awt.EventQueue$4.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Sour
ce)
        at java.awt.EventQueue.dispatchEvent(Unknown Source)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
        at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
        at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
        at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
        at java.awt.EventDispatchThread.run(Unknown Source)
请问这个是什么原因？？java 监听

Answer 1

试试这个。
((JButton)event.getSource()).setText("I've been click");

Answer 2

抛空指针错的原因一般是某个成员变量没有初始化JButton button;这条语句没有初始化

Answer 3

 JButton button=new JButton("click me");
=》 button=new JButton("click me");

Answer 4

你的成员属性button初始化了？你到底
想对哪一个按钮注册监听？！
是成员变量button？还是go方法中的button？

Answer 5

JButton button=new JButton("click me");改成
button=new JButton("click me");