Calculator.java

import java.awt.event.*;
import javax.swing.*;
import java.awt.*;

public class Calculator extends JFrame implements ActionListener {
    static JFrame f;
    static JTextField l;
    String s0, s1, s2;
    Calculator() {
        s0 = s1 = s2 = " ";
    }

    public static void main(String[] args) {
        f = new JFrame("swing calculator");
        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());

        } catch (Exception e) {
            System.err.println(e.getMessage());

        }

        Calculator c = new Calculator();
        l = new JTextField(16);
        l.setEditable(false);


        JButton b0, b1, b2, b3, b4, b5, b6, b7, b8, b9, ba, bs, bd, bm, beq, beql, be;

        b0 = new JButton("0");
        b1 = new JButton("1");
        b2 = new JButton("2");
        b3 = new JButton("3");
        b4 = new JButton("4");
        b5 = new JButton("5");
        b6 = new JButton("6");
        b7 = new JButton("7");
        b8 = new JButton("8");
        b9 = new JButton("9");

        beql = new JButton("=");
        ba = new JButton("+");
        bs = new JButton("-");
        bd = new JButton("/");
        bm = new JButton("*");
        beq = new JButton("c");
        be = new JButton(".");


        JPanel p = new JPanel();


        bm.addActionListener(c);
        bd.addActionListener(c);
        bs.addActionListener(c);
        ba.addActionListener(c);
        beql.addActionListener(c);
        be.addActionListener(c);
        beq.addActionListener(c);

        b0.addActionListener(c);
        b1.addActionListener(c);
        b2.addActionListener(c);
        b3.addActionListener(c);
        b4.addActionListener(c);
        b5.addActionListener(c);
        b6.addActionListener(c);
        b7.addActionListener(c);
        b8.addActionListener(c);
        b9.addActionListener(c);

        p.add(l);
        p.add(b0);
        p.add(b1);
        p.add(b2);
        p.add(b3);
        p.add(b4);
        p.add(b5);
        p.add(b6);
        p.add(b7);
        p.add(b8);
        p.add(b9);
        p.add(ba);
        p.add(bs);
        p.add(bm);
        p.add(bd);
        p.add(beq);
        p.add(beql);
        p.add(be); 

        p.setBackground(Color.BLUE);
        f.add(p);
        f.setSize(200, 220);
        f.show();
    }

    public void actionPerformed(ActionEvent e) {
        String s = e.getActionCommand();
        System.out.println(s);
        if (s.charAt(0) >= '0' && s.charAt(0) <= '9' || s.charAt(0) == '.') {
            if (!s1.equals(" "))
                s2 = s2 + s;
            else
                s0 = s0 + s;
            l.setText(s0 + s1 + s2);
        } else if (s.charAt(0) == 'c') {
            s0 = s1 = s2 = " ";
            l.setText(s0 + s1 + s2);
        } else if (s.charAt(0) == '=') {
            Double te;
            if (s1.equals("+"))
                te = (Double.parseDouble(s0) + Double.parseDouble(s2));
            else if (s1.equals("-"))
                te = (Double.parseDouble(s0) - Double.parseDouble(s2));
            else if (s1.equals("/"))
                te = (Double.parseDouble(s0) / Double.parseDouble(s2));
            else
                te = (Double.parseDouble(s0) * Double.parseDouble(s2));

            s0 = Double.toString(te);
            s1 = " ";
            s2 = " ";
        } else {
            s1 = s;
            l.setText(s0 + s1 + s2);
        }

        l.setText(s0 + s1 + s2);


    }

}