PROGRAM KALKULATOR PADA JAVA

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

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

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);
}
}