Program Java Konversi suhu [GUI]

import javax.swing.*;
import java.awt.event.ActionListener;
public class konversi_suhu{
    public konversi_suhu(){
        JFrame f=new JFrame();
        f.setTitle("Konversi suhu");
        f.setLayout(null);
        f.setSize(300,300);
       
        JLabel lb1=new JLabel("Celcius");
        JLabel lb2=new JLabel("Fahreheit");
        JLabel lb3=new JLabel("Kelvin");
        JLabel lb4=new JLabel("Reamur");
       
        JButton jb=new JButton("Konversi suhu");
       
        final JTextField jt1=new JTextField();
        final JTextField jt2=new JTextField();
        final JTextField jt3=new JTextField();
        final JTextField jt4=new JTextField();
       
        f.add(lb1); lb1.setBounds(20,30,100,25);
        f.add(jt1); jt1.setBounds(120,30,100,25);
        f.add(jb);  jb.setBounds(60,60,120,25);
        f.add(lb2); lb2.setBounds(20,90,100,25);
        f.add(jt2); jt2.setBounds(120,90,100,25);
        f.add(lb3); lb3.setBounds(20,120,100,25);
        f.add(jt3); jt3.setBounds(120,120,100,25);
        f.add(lb4); lb4.setBounds(20,150,100,25);
        f.add(jt4); jt4.setBounds(120,150,100,25);
       
        jb.addActionListener(new java.awt.event.ActionListener (){
            public void actionPerformed(java.awt.event.ActionEvent evt){
                int input=Integer.parseInt(jt1.getText());
                double k=input+273.15;
                double f=input*1.8+32;
                int r=(input*80)/100;
               
                jt2.setText(String.valueOf(f));
                jt3.setText(String.valueOf(k));
                jt4.setText(String.valueOf(r));
               
            }
        });

        f.setVisible(true);
    }
    public static void main(String [] lx){
        konversi_suhu manggil=new konversi_suhu();
    }  
}

Outputnya