Question

java程序菜鸟问题

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

class button{
JFrame c =new JFrame("Welcome!");
JButton a=new JButton("hello!");
JCheckBox b=new JCheckBox("hi!");
JLabel f=new JLabel("chose a button plz!");

public button(){
a.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent ae){f.setText("you chose a normal button!");
}
});

c.getContentPane().add(f);
c.getContentPane().add(a);
c.getContentPane().add(b);
c.getContentPane().setLayout(new java.awt.FlowLayout());

c.setSize(200,250);
c.setVisible(true);
c.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

public static void main(String args[]){
button d=new button();

}
}

--------------------
其中a.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent ae){f.setText("you chose a normal button!");
}
});这段，为什么放在构造函数的上面（就是构造之前的那段域里，换报错呢？错误信息是identifier expected

为什么啊～～～～
我不明白的是贴的这段是能编译通过的，就是不知道为什么放在构造方法之前的域会报错@@

Answer 1

开头应该这样写：
class button implements ActionListener{

/*more code*/

}

Answer 2

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

class button{

JFrame c =new JFrame("Welcome!");
JButton a=new JButton("hello!");
JCheckBox b=new JCheckBox("hi!");
JLabel f=new JLabel("chose a button plz!");

public button()
{
a.addActionListener(
new ActionListener()
{
public void actionPerformed(ActionEvent ae)
{
f.setText("you chose a normal button!");
}
});

c.getContentPane().add(f);
c.getContentPane().add(a);
c.getContentPane().add(b);
c.getContentPane().setLayout(new java.awt.FlowLayout());

c.setSize(200,250);
c.setVisible(true);
c.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}

public static void main(String args[])
{
button d=new button();

}
}