Bilangan Terbesar (Materi Applet Java)

import java.applet.Applet;
import java.awt.Graphics;
import javax.swing.*;
public class appletbilterbesar extends Applet {
double max;
    public void init() {
        String firstnumber;
        String secondnumber;
        String thirdnumber;
        double n1;
        double n2;
        double n3;
        firstnumber = JOptionPane.showInputDialog("Masukkan Angka Pertama");
        secondnumber = JOptionPane.showInputDialog("Masukkan Angka Kedua");
        thirdnumber = JOptionPane.showInputDialog("Masukkan Angka Ketiga");
        n1=Double.parseDouble(firstnumber);
        n2=Double.parseDouble(secondnumber);
        n3=Double.parseDouble(thirdnumber);
        if (n1>n2 && n1>n3){
            max=n1;
        } else
            if(n2>n1 && n2>n3){
                max = n2;
            } else {
                max = n3;
            }
    }
 public void paint(Graphics g)
    {
     super.paint(g);
     g.drawRect(15,10,270,20);
     g.drawString("Bilangan Terbesar Adalah " +max, 25,25);
 }

}