Hello Friend,

Try the following code:

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
class  ButtonAction extends JFrame implements ActionListener{
    JButton b1,b2,b3,b4;
    ButtonAction(){
    b1=new JButton("A");
    b2=new JButton("B");
    b3=new JButton("C");
    b4=new JButton("D");
    b1.addActionListener(this);
    b2.addActionListener(this);
    b3.addActionListener(this);
    b4.addActionListener(this);
    JPanel p=new JPanel();
    p.add(b1);
    p.add(b2);
    p.add(b3);
    p.add(b4);
    add(p);
    setVisible(true);
    pack();
    }
public void actionPerformed(ActionEvent e){
    String choice=e.getActionCommand();
    if(choice.equals("A")){
        JOptionPane.showMessageDialog(null,"This is button A");
    }
else if(choice.equals("B")){
    JOptionPane.showMessageDialog(null,"This is button B");
}
else if(choice.equals("C")){
    JOptionPane.showMessageDialog(null,"This is button C");
}
else if(choice.equals("D")){
    JOptionPane.showMessageDialog(null,"This is button D");
}
}
public static void main(String[] args){
     new ButtonAction();
    }
}

Thanks