AWT based Java program to implement basic calculator

Calculator Program in Java:

import java.awt.*;
import java.awt.event.*;
class Calculator extends Frame implements ActionListener
{
TextField tfInput;
Panel panel;
String btnString[] = {"7", "8", "9", "+",
"4", "5", "6", "-",
"1", "2", "3", "*",
"C", "0", "=", "/"};
Button btn[] = new Button[16];
int num1 = 0, num2 = 0, result = 0;
char op;
public Calculator() {
Font f = new Font("Cambria", Font.BOLD, 18);
tfInput = new TextField(10);
tfInput.setFont(f);
panel = new Panel();
add(tfInput, "North");
add(panel, "Center");
panel.setLayout(new GridLayout(4,4));
for(int i=0; i < 16; i++) {
btn[i] = new Button(btnString[i]);
btn[i].setFont(f);
btn[i].addActionListener(this);
panel.add(btn[i]);
}
addWindowListener(new WindowAdapter(){
public void windowClosing(WindowEvent we) {
System.exit(0);
}
});
}
public void actionPerformed(ActionEvent ae) {
String str = ae.getActionCommand();
if(str.equals("+")) {
op = '+';
num1 = Integer.parseInt(tfInput.getText());
tfInput.setText("");
}
else if(str.equals("-")) {
op = '-';
num1 = Integer.parseInt(tfInput.getText());
tfInput.setText("");
}
else if(str.equals("*")) {
op = '*';
num1 = Integer.parseInt(tfInput.getText());
tfInput.setText("");
}
else if(str.equals("/")) {
op = '/';
num1 = Integer.parseInt(tfInput.getText());
tfInput.setText("");
}
else if(str.equals("=")) {
num2 = Integer.parseInt(tfInput.getText());
switch(op) {
case '+' : result = num1 + num2;
break;
case '-' : result = num1 - num2;
break;
case '*' : result = num1 * num2;
break;
case '/' : result = num1 / num2;
break;
}
tfInput.setText(result + "");
result = 0;
}
else if(str.equals("C")) {
tfInput.setText("");
num1 = num2 = result = 0;
}
else {
tfInput.setText(tfInput.getText() + str);
}
}
public static void main(String args[]) {
Calculator c1 = new Calculator();
c1.setTitle("Calculator");
c1.setSize(250,300);
c1.setVisible(true);
}
}

 

Output: