我的程序代码编译通不过

我是java新手，好多都不懂，下面是我自己编的简单程序代码我找不出错误，但是编译通不过，提示监听那有错误，请帮忙更正一下。
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Demo extends JFrame {

public Demo(String t) {
super(t);
Container contentPane=this.getContentPane();
contentPane.setLayout(new FlowLayout());
setBackground(Color.white);
}

JButton a1=new JButton("demo1");
JButton a2=new JButton("demo2");
JButton a3=new JButton("demo3");
JLabel a4=new JLabel("demo4");
a1.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e){a4.setText("xu");}
});
a2.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e){a4.setText("xian");}
});
a3.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e){a4.setText("yue");}
});



/**
* @param args the command line arguments
*/
public static void main(String[] args) {
Demo beat =new Demo("good");

}

}
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经过我多次修改成功了，相当感谢。

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可以这样,这是匿名类的用法!

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怎么可以?

在类里面只能声明变量,你要做别的事情,必须放到方法里面或者初始化块里面

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好象在类里面真不能添加监听器，我试过了，放在方法里面就行了

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我弄错了,呵呵!

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把想做的事情要么放在static语句块，要么放在方法里，因为放在类里，你怎么通过对象来发送消息呢？呵呵

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import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Demo extends JFrame //implements ActionListener 为什么不实现接口啊!
{
private static final long serialVersionUID = 1L;
public dfdfds(String t) {
super(t);
Container contentPane=this.getContentPane();
contentPane.setLayout(new FlowLayout());
setBackground(Color.white);
}

JButton a1=new JButton("demo1");
JButton a2=new JButton("demo2");
JButton a3=new JButton("demo3");
JLabel a4=new JLabel("demo4");
a1.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e){a4.setText("xu");}
});
a2.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e){a4.setText("xian");}
});
a3.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e){a4.setText("yue");}
});



public static void main(String[] args) {
dfdfds beat =new dfdfds("good");

}

}
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都完事了啊!
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