Income Tax Calculator

Here is the java code:

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

public class IncomeTaxCalculator extends Applet
implements ActionListener,WindowListener{

    private Label label,label1,label2,label3;
    private JTextField txt,txt1,txt3,txt4;
    private JButton btn1,btn2;
  
    public void init(){
        Frame f=new Frame();
        Frame f1=new Frame();
        f.setLayout(new BorderLayout());
        f.setSize(1000, 300);
        Panel p=new Panel();
        Panel pc1=new Panel();
        //pc.setLayout(new BorderLayout());
        f.add(pc1,"South");
        f.add(p,"North");
        label=new Label("Enter Income  :");
        label1=new Label("Tax To Be Paid :");
        label2=new Label("Cess");
        label3=new Label("Income Tax");
        txt1=new JTextField(10);
        txt3=new JTextField(10);
        txt4=new JTextField(10);
        txt=new JTextField(10);
        p.add(label);
        p.add(txt);
        p.add(label3);
        p.add(txt4);
        p.add(label2);
        p.add(txt3);
        p.add(label1);
        p.add(txt1);
        btn1= new JButton("SUBMIT");
        btn2= new JButton("EXIT");
        pc1.add(btn1);
        pc1.add(btn2);
        f.setVisible(true);
        btn1.addActionListener(this);
        btn2.addActionListener(this);
        }
  
    public static void main(String args[]){
        new IncomeTaxCalculator().init();
    }
    @Override
    public void actionPerformed(ActionEvent e) {
        // TODO Auto-generated method stub
        JButton btn=(JButton)e.getSource();
        if(btn==btn1){
            double a=Integer.parseInt(txt.getText());
            double tax=0,b=0;
          
            if(a>0 && a<=160000){ //Change the Income here
                txt1.setText("0");
                txt4.setText("0");
                txt3.setText("0");
              
            }else if(a>160000 && a<=300000){ //Change the Income here
                a=a-160000;
                tax=0.1*a; //Change the rate % here
                txt4.setText(String.valueOf(tax));
                txt3.setText(String.valueOf(tax*.03));
                tax+=tax*.03;
                txt1.setText(String.valueOf(tax));
            }else if(a>300000 && a<=500000){ //Change the Income here
                a=a-300000;
                tax=0.2*a+14000; //Change the rate % here
                txt4.setText(String.valueOf(tax));
                txt3.setText(String.valueOf(tax*.03));
                tax+=tax*.03;
                txt1.setText(String.valueOf(tax));
            }else if(a>500000){ //Change the Income here
                a=a-500000;
                tax=0.3*a+54000; //Change the rate % here
                txt4.setText(String.valueOf(tax));
                txt3.setText(String.valueOf(tax*.03));
                tax+=tax*.03;
                txt1.setText(String.valueOf(tax));
            }
        }else if(btn==btn2){
            System.exit(0);
        }
    }
    @Override
    public void windowActivated(WindowEvent e) {
        // TODO Auto-generated method stub
      
    }
    @Override
    public void windowClosed(WindowEvent e) {
        // TODO Auto-generated method stub
      
    }
    @Override
    public void windowClosing(WindowEvent e) {
        // TODO Auto-generated method stub
      
    }
    @Override
    public void windowDeactivated(WindowEvent e) {
        // TODO Auto-generated method stub
      
    }
    @Override
    public void windowDeiconified(WindowEvent e) {
        // TODO Auto-generated method stub
      
    }
    @Override
    public void windowIconified(WindowEvent e) {
        // TODO Auto-generated method stub
      
    }
    @Override
    public void windowOpened(WindowEvent e) {
        // TODO Auto-generated method stub
      
    }
}