Java AWT 编程 空指针异常 哪里出错了？
RT
源代码：

Java code

package TEST;import java.awt.*;import java.awt.event.*;import java.text.MessageFormat;public class Start implements ActionListener{    TextField user;    TextField password;    public Start(){       Frame f = new Frame("登录界面");       f.setLayout(new BorderLayout());       Panel p1 = new Panel();       p1.setLayout(new GridLayout(2,1));       p1.add(new Label("用户名："));       p1.add(new Label("密码："));       Panel p2 = new Panel();       p2.setLayout(new GridLayout(2,1));       TextField user = new TextField();       TextField password = new TextField(10);       password.setEchoChar('*');       user.addActionListener(this);       password.addActionListener(this);       p2.add(user);       p2.add(password);       Panel p3 = new Panel();       p3.setLayout(new FlowLayout());       Button submit = new Button("确定");       Button reset = new Button("重置");       submit.addActionListener(this);       reset.addActionListener(this);       p3.add(submit);       p3.add(reset);       f.add(p1,BorderLayout.WEST);       f.add(p2,BorderLayout.CENTER);          f.add(p3,BorderLayout.SOUTH);       f.add(new Label("请输入你的用户信息："),BorderLayout.NORTH);       f.setVisible(true);       f.setLocation(320,240);       f.pack();       f.addWindowListener(new FormAdapter());    }    public static void main(String[] args) {        // TODO Auto-generated method stub        Start st = new Start();    }    private class FormAdapter extends WindowAdapter{        public void windowClosing(WindowEvent e){            System.exit(0);        }    }    //@Override    public void actionPerformed(ActionEvent e) {        // TODO Auto-generated method stub        String str = e.getActionCommand();        if(str.equals("确定")){            System.out.println(str);            System.out.println(user.getText());            //System.out.println(password.getText());        }else if(str.equals("重置")){            System.out.println(str);        }    }}

Java code

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException    at TEST.Start.actionPerformed(Start.java:58)    at java.awt.Button.processActionEvent(Unknown Source)    at java.awt.Button.processEvent(Unknown Source)    at java.awt.Component.dispatchEventImpl(Unknown Source)    at java.awt.Component.dispatchEvent(Unknown Source)    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)    at java.awt.EventQueue.access$000(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 Source)    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)    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 Source)    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)

[解决办法]
System.out.println(user.getText());
这句报错

你的TextField user 没有实例
[解决办法]
TextField user = new TextField();

改成 user = new TextField();
你上面已经申明了 不要再申明
[解决办法]
把下面两句 TextField user = new TextField();
TextField password = new TextField(10);
修改为 user = new TextField();
password = new TextField(10);
你调用的是全局变量的user和这里的user不是一个对象