Не работают кнопки - Java

import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
 
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JTextField;
import javax.swing.JFrame;
public class k extends JFrame {
    JButton b1,b2,b3,b4,b5,b6,b7,b8,b9;
    JLabel l1,l2,l3;
    JTextField t1;
    long a,b;
    String as,bs;
    kh han = new kh();
 public k (String s){
     super(s);
     setLayout(new FlowLayout());
     l1 = new JLabel("||Первое число||");
     l2 = new JLabel("||Второе число||");
     l3 = new JLabel("||Ответ|| ");
     add(l1);add(l2);add(l3);
     b1 = new JButton("1");
     b2 = new JButton("2");
     b3 = new JButton("3");
     b4 = new JButton("4");
     b5 = new JButton("5");
     b6 = new JButton("6");
     b7 = new JButton("7");
     b8 = new JButton("8");
     b9 = new JButton("9");
     add(b1);add(b2);add(b3);add(b4);add(b5);add(b6);add(b7);add(b8);add(b9);
     b2.addActionListener(han);
     b1.addActionListener(han);
     
 }
 public class kh implements ActionListener{
     public void actionPerformed(ActionEvent e) {
         if (e.getSource()==b1) {a = a*10+1;as = ""+a;l1.setText(as);}
         if (e.getSource()==b2) {a = a*10+2;as = ""+a;l1.setText(as);}
         if (e.getSource()==b3) {a = a*10+3;as = ""+a;l1.setText(as);}
         if (e.getSource()==b4) {a = a*10+4;as = ""+a;l1.setText(as);}
         if (e.getSource()==b5) {a = a*10+5;as = ""+a;l1.setText(as);}
         if (e.getSource()==b6) {a = a*10+6;as = ""+a;l1.setText(as);}
         if (e.getSource()==b7) {a = a*10+7;as = ""+a;l1.setText(as);}
         if (e.getSource()==b8) {a = a*10+8;as = ""+a;l1.setText(as);}
         if (e.getSource()==b9) {a = a*10+9;as = ""+a;l1.setText(as);}

  }
 }
}

import javax.swing.JFrame;
public class k2 {
     public static void main (String [] args){
         k ka = new k("Калькулятор");
         ka.setVisible(true);
         ka.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         ka.setSize(300,300);
         ka.setResizable(false);
         ka.setLocationRelativeTo(null);
     }
 
}