Button Array in java swing with Action Perform

Button Array in java swing with Action Perform 

import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPopupMenu;
import javax.swing.JTextField;

class MultiButton extends JFrame implements ActionListener
{
          int i;
           int n=20;
         JButton[] b1 = new JButton[12];
         JTextField[] t1=new JTextField[12];
         String s1[]={"A","B","C","D","E","F","G","H","I","J","K","M","N","O","P"};
          JPopupMenu jp;
    MultiButton()
    {
   
        for(i=0;i<12;i++)
        {
         
         
           b1[i]=new JButton(s1[i]);
           add(b1[i]);
           b1[i].addActionListener(this);
           b1[i].setBounds(10,n,70,30);
           n+=50;

        }
        setLayout(null);
       
        //setLayout(new GridLayout(6, 5));

    }
   
       
      public void actionPerformed(ActionEvent e)
      {
   
            if(e.getSource()==b1[0])
              //  JOptionPane.showMessageDialog(this,s1[0]);
                System.out.println(s1[0]);
            if(e.getSource()==b1[1])
               //JOptionPane.showMessageDialog(this,s1[1]); 
                System.out.println(s1[1]);
            if(e.getSource()==b1[2])
               // JOptionPane.showMessageDialog(this,s1[2]); 
                System.out.println(s1[3]);
            if(e.getSource()==b1[3])
             //JOptionPane.showMessageDialog(this,s1[3]); 
            //JOptionPane.showConfirmDialog(this,"hello");
               // System.out.println(s1[4]);
                b1[0].setText(s1[2]);
           
      }
   
    public static void main(String[] args)
    {
        MultiButton mb=new MultiButton();
        mb.setVisible(true);
        mb.setTitle("buttons");
        mb.setSize(550,660);
    }
}