Simple Calculator (using AWT)

/**
 * Simple Calculator (using AWT)
 * Date : 10.08.19
 */
package AWT;
import java.awt.*;
import java.awt.event.*;

public class Calculator implements ActionListener {
    TextField tf1, tf2, tf3;
    Button b1, b2, b3, b4;
    Calculator(){
        Frame f = new Frame("Calculator");
        f.setSize(300, 300);
        f.setLayout(null);
        f.setVisible(true);
        Label l1 = new Label("Input 1: ");
        l1.setBounds(50, 50, 40, 20);
        Label l2 = new Label("Input 2: ");
        l2.setBounds(50, 110, 40, 20);
        Label l3 = new Label("Output: ");
        l3.setBounds(50, 170, 40, 20);

        tf1 = new TextField();
        tf1.setBounds(100, 50, 100, 20);

        tf2 = new TextField();
        tf2.setBounds(100, 110, 100, 20);

        tf3 = new TextField();
        tf3.setBounds(100, 170, 100, 20);
        tf3.setEditable(false);

        b1 = new Button("+");
        b1.setBounds(50, 200, 30, 30);
        b1.addActionListener(this);

        b2 = new Button("-");
        b2.setBounds(90, 200, 30, 30);
        b2.addActionListener(this);

        b3 = new Button("*");
        b3.setBounds(130, 200, 30, 30);
        b3.addActionListener(this);

        b4 = new Button("/");
        b4.setBounds(170, 200, 30, 30);
        b4.addActionListener(this);

        f.add(tf1); f.add(tf2); f.add(tf3);
        f.add(l1); f.add(l2); f.add(l3);
        f.add(b1); f.add(b2); f.add(b3); f.add(b4);
    }

    public void actionPerformed(ActionEvent e){
        String in1 = tf1.getText();
        String in2 = tf2.getText();
        double a = Double.parseDouble(in1);
        double b = Double.parseDouble(in2);
        double c = 0;
        if(e.getSource() == b1){ c = a + b; }
        else if(e.getSource() == b2){ c = a - b; }
        else if(e.getSource() == b3){ c = a * b; }
        else if(e.getSource() == b4){ c = a / b; }
        String result = String.valueOf(c);
        tf3.setText(result);
    }

    public static void main(String[] args){
        new Calculator();
    }
}