// https://www.facebook.com/groups/JavaBr/permalink/13271875172

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

public class Exemplo0505 extends JFrame implements ActionListener {
    private static final long serialVersionUID = 1L;
    JLabel L1, L2, L3;
    JButton B1, B2, B3, B4, B5;
    JTextField T1, T2, T3;

    public static void main(String args[]) {
        JFrame Janela = new Exemplo0505();
        Janela.setVisible(true);
        WindowListener x = new WindowAdapter() {
            // você precisa sobrescrever algum método
            // System.exit(0);
        };

        Janela.addWindowListener(x);

    }

    Exemplo0505() {
        setTitle("calculadora");
        setSize(350, 90);
        setLocation(50, 50);

        getContentPane().setBackground(new Color(150, 150, 150));
        getContentPane().setLayout(new GridLayout(3, 4));

        L1 = new JLabel("num1");
        L1.setForeground(Color.black);
        L2 = new JLabel("num2");
        L2.setForeground(Color.black);
        L2.setFont(new Font("", Font.BOLD, 14));
        L3 = new JLabel("total");
        L3.setFont(new Font("", Font.BOLD, 14));

        B1 = new JButton("+");
        B1.addActionListener(this);
        B2 = new JButton("-");
        B2.addActionListener(this);
        B3 = new JButton("*");
        B3.addActionListener(this);
        B4 = new JButton("/");
        B4.addActionListener(this);
        B5 = new JButton("LImPAR");
        B5.addActionListener(this);
        B5.setBackground(Color.black);
        B5.setForeground(Color.white);

        T1 = new JTextField();
        T2 = new JTextField();
        T3 = new JTextField();

        getContentPane().add(L1);
        getContentPane().add(T1);
        getContentPane().add(B1);
        getContentPane().add(L2);
        getContentPane().add(T2);
        getContentPane().add(B2);
        getContentPane().add(L3);
        getContentPane().add(T3);
        getContentPane().add(B3);
        getContentPane().add(B4);
        getContentPane().add(B5);
    }

    public void actionperformed(ActionEvent e) {
        if (e.getSource() == B5) {
            T1.setText("");
            T2.setText("");
            T3.setText("");
            return;
        }
        Float N1 = 0f, N2 = 0f, result = 0f;
        try {
            N1 = Float.parseFloat(T1.getText());
            N2 = Float.parseFloat(T2.getText());
        } catch (NumberFormatException Error) {
            T3.setText("Erro");
            return;
        }
        if (e.getSource() == B1) {
            result = N1 + N2;
        } else if (e.getSource() == B2) {
            result = N1 - N2;
        } else if (e.getSource() == B3) {
            result = N1 * N2;
        } else if (e.getSource() == B4) {
            result = N1 / N2;
        }
        T3.setText("" + result);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        // faltava implementar esse método, mas pq essa classe é um
        // actionlistener?

    }
}