Winston Tutorial 13-16 Calculator

package com.samkough.main;

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

@SuppressWarnings("serial")
public class Win extends JFrame implements ActionListener
{
	private static final int WIDTH = 250;
	private static final int HEIGHT = 175;

	JButton add, subtract, multiply, divide, sqrt;
	JTextField num1, num2;
	JLabel result, enter1, enter2;

	public Win()
	{
		// this layout allows you to create a layout anyway you want basically
		setLayout(new GridBagLayout());
		// this will be for padding and whatnot
		GridBagConstraints c = new GridBagConstraints();

		enter1 = new JLabel("1st: ");
		c.fill = GridBagConstraints.HORIZONTAL;
		c.gridx = 0;
		c.gridy = 0;
		add(enter1, c);

		num1 = new JTextField(10);
		c.fill = GridBagConstraints.HORIZONTAL;
		c.gridx = 1;
		c.gridy = 0;
		c.gridwidth = 3;
		add(num1, c);

		enter2 = new JLabel("2nd: ");
		c.fill = GridBagConstraints.HORIZONTAL;
		c.gridx = 0;
		c.gridy = 1;
		c.gridwidth = 1;
		add(enter2, c);

		num2 = new JTextField(10);
		c.fill = GridBagConstraints.HORIZONTAL;
		c.gridx = 1;
		c.gridy = 1;
		c.gridwidth = 3;
		add(num2, c);

		add = new JButton("+");
		c.fill = GridBagConstraints.HORIZONTAL;
		c.gridx = 0;
		c.gridy = 2;
		c.gridwidth = 1;
		add(add, c);

		subtract = new JButton("-");
		c.fill = GridBagConstraints.HORIZONTAL;
		c.gridx = 1;
		c.gridy = 2;
		add(subtract, c);

		multiply = new JButton("*");
		c.fill = GridBagConstraints.HORIZONTAL;
		c.gridx = 2;
		c.gridy = 2;
		add(multiply, c);

		divide = new JButton("/");
		c.fill = GridBagConstraints.HORIZONTAL;
		c.gridx = 3;
		c.gridy = 2;
		add(divide, c);

		result = new JLabel("");
		c.fill = GridBagConstraints.HORIZONTAL;
		c.gridx = 0;
		c.gridy = 4;
		c.gridwidth = 4;
		add(result, c);

		add.addActionListener(this);
		subtract.addActionListener(this);
		multiply.addActionListener(this);
		divide.addActionListener(this);
	}

	public void actionPerformed(ActionEvent e)
	{
		double n1, n2;

		try
		{
			n1 = Double.parseDouble(num1.getText());
		}
		catch(NumberFormatException e1)
		{
			result.setText("Illegal character for 1st textbox!");
			result.setForeground(Color.RED);
			return;
		}

		try
		{
			n2 = Double.parseDouble(num2.getText());
		}
		catch(NumberFormatException e2)
		{
			result.setText("Illegal character for 2nd textbox!");
			result.setForeground(Color.RED);
			return;
		}

		// this is gonna help validate what button the user presses
		String op = e.getActionCommand();

		// this is the math logic for the symbols
		if (op.equals("+"))
		{
			double sum = n1 + n2;
			result.setText(n1 + " + " + n2 + " = " + sum);
			result.setForeground(Color.BLUE);
		}
		else if (op.equals("-"))
		{
			double difference = n1 - n2;
			result.setText(n1 + " - " + n2 + " = " + difference);
			result.setForeground(Color.BLUE);
		}
		else if (op.equals("*"))
		{
			double product = n1 * n2;
			result.setText(n1 + " * " + n2 + " = " + product);
			result.setForeground(Color.BLUE);
		}
		else if (op.equals("/"))
		{
			// we make an if because you can't divide by zero
			if (n2 == 0)
			{
				result.setText("Cannot divide by zero!");
				result.setForeground(Color.RED);
			}
			else
			{
				double quotient = n1 / n2;
				result.setText(n1 + " / " + n2 + " = " + quotient);
				result.setForeground(Color.BLUE);
			}
		}
	}

	public static void main(String args[])
	{
		Win frame = new Win();

		frame.setVisible(true);
		frame.setSize(WIDTH, HEIGHT);
		// frame.pack();
		frame.setTitle("Calculator");
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setLocationRelativeTo(null);
	}
}