这是怎么回事啊

[chiruchiru]

E:\JavaWork>javac EventTest.java

E:\JavaWork>java EventTest
Exception in thread "main" java.lang.NullPointerException
at java.awt.Container.addImpl(Container.java:1010)
at java.awt.Container.add(Container.java:348)
at EventTest.<init>(EventTest.java:29)
at EventTest.main(EventTest.java:44)



源代码

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

public class EventTest
{
JFrame frame;
JPanel panel;
JButton btnAdd;
JButton btnDelete;
JButton btnModify;
JLabel lblStatus;
FlowLayout fl;

EventTest()
{
frame=new JFrame("Event Test!!");
panel=(JPanel)frame.getContentPane();
fl=new FlowLayout();
panel.setLayout(fl);

btnAdd=new JButton("Add User");
btnDelete=new JButton("Delete User");
btnAdd=new JButton("Modify User");
lblStatus=new JLabel();

panel.add(btnAdd);
panel.add(btnDelete);
panel.add(btnModify);
panel.add(lblStatus);

ButtonHander bh=new ButtonHander();
btnAdd.addActionListener(bh);
btnDelete.addActionListener(bh);
btnModify.addActionListener(bh);

frame.pack();
frame.setVisible(true);


}
public static void main(String args[])
{
new EventTest();
}

class ButtonHander implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
Object obj=e.getSource();

if(obj==btnAdd)
{
lblStatus.setText("Add Button Clicked!!");
}
if(obj==btnDelete)
{
lblStatus.setText("Delete Button Clicked!!");
}
if(obj==btnModify)
{
lblStatus.setText("Modify Button Clicked!!");
}
}
}
}

哪里空指针异常了 实在是找不到

[Ganymede]

你的btnModify只是声明，没有new 出来

[JamesLiu]

btnAdd=new JButton("Add User");
btnDelete=new JButton("Delete User");
btnAdd=new JButton("Modify User");//这一行


-------------------------------
编程菜鸟学堂QQ群144648357

[Nodin]

btnAdd=new JButton("Add User");
btnDelete=new JButton("Delete User");
btnAdd=new JButton("Modify User");//此处应该是btnModify

btnModify.addActionListener(bh);//由于上面未对btnModify实例化，导致空指针异常

[tanrenzong1986]

btnModify需要实例化

[部落联盟]

细心点.....

[zqfddqr]

没有生成对象

[铁匠梁老师]

debug模式一目了然

[chiruchiru]

哎 我真是太马虎了 谢谢你们