Program Kalkulator GUI Culun Menggunakan Java AWT

Berikut kode sumber program kalkulator berbasis grafis menggunakan Java AWT. Kenapa culun? karena memang culun... ngga percaya? coba aja sendiri!

import java.awt.*;
import java.awt.event.*;

public class Kalkulator extends Frame implements WindowListener, ActionListener {
  TextField txtBil1, txtOpr, txtBil2, txtHasil;
  Button btnHitung;

  /** Creates a new instance of Kalkulator */
  public Kalkulator(String judul) {
      super(judul);
      this.addWindowListener(this);
      this.setLayout(new FlowLayout(FlowLayout.LEFT,10,10));
      txtBil1 = new TextField();
      txtBil1.setColumns(5);
      txtOpr = new TextField();
      txtOpr.setColumns(5);
      txtBil2 = new TextField();
      txtBil2.setColumns(5);
      txtHasil = new TextField();
      txtHasil.setColumns(5);
      btnHitung = new Button(" = ");
      btnHitung.addActionListener(this);
      add(txtBil1);
      add(txtOpr);
      add(txtBil2);
      add(btnHitung);
      add(txtHasil);
  }
  public void windowActivated(WindowEvent e) {}
  public void windowClosed(WindowEvent e) {}
  public void windowClosing(WindowEvent e) {
      setVisible(false);
      System.exit(0);
  }
  public void windowDeactivated(WindowEvent e) {}
  public void windowDeiconified(WindowEvent e) {}
  public void windowIconified(WindowEvent e) {}
  public void windowOpened(WindowEvent e) {}

  public void actionPerformed(ActionEvent e) {
      double a, b, hasil;
      String c;
      if (e.getSource() == btnHitung){
          a = Double.parseDouble(txtBil1.getText());
          b = Double.parseDouble(txtBil2.getText());
          c = txtOpr.getText();
          if (c.equals("*")) {
              hasil = a * b;
          } else if (c.equals("/")) {
              hasil = a / b;
          } else if (c.equals("+")) {
              hasil = a + b;
          } else if (c.equals("-")) {
              hasil = a - b;
          } else {
              hasil = 0;
          }
        
          txtHasil.setText(""+hasil);
      }
  }

  public static void main(String args[]) {
      Kalkulator frm = new Kalkulator("Kalkulator Culun");
      frm.setSize(500, 200);
      frm.setVisible(true);
  }
}