Calculator.java

package com.tinkeracademy.projects;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.math.RoundingMode;
import java.text.DecimalFormat;
import java.util.Stack;

import javax.swing.JButton;
import javax.swing.JTextArea;

public class Calculator implements ActionListener {
	
	public Stack<String> inputs = new Stack<String>();
	
	public JTextArea output;

	public static void main(String[] args) {
		Calculator calculator = new Calculator();
		javax.swing.SwingUtilities.invokeLater(new Runnable() {
			public void run() {
				calculator.createAndShowGUI();
			}
		});
	}

	public void createAndShowGUI() {
		Window.show();
		Window.addLabel("Calculator Application Developed By: Tinker Academy v1.0");
		output = Window.addTextArea("0", 2, 10, false);
		String[][] controls = {
				{ "7", "8", "9", "AC" },
				{ "4", "5", "6", "-" }, 
				{ "1", "2", "3", "+" },
				{ "0", "\u00F7", "*", "=" } 
		};
		JButton[][] buttons = Window.addGridButtons(controls);
		for (int i = 0; i < buttons.length; i++) {
			JButton[] innerArray = buttons[i];
			for (int j = 0; j < innerArray.length; j++) {
				JButton button = innerArray[j];
				button.addActionListener(this);
			}
		}
	}

	@Override
	public void actionPerformed(ActionEvent e) {
		System.out.println(e.getActionCommand());
		if ("AC".equals(e.getActionCommand())) {
			output.setText("0");
			inputs.clear();
		} else if ("=".equals(e.getActionCommand())) {
			String answer = calculate();
			output.setText(answer);
			inputs.clear();
		} else {
			if (inputs.isEmpty()) {
				output.setText(e.getActionCommand());
			} else {
				output.setText(output.getText() + e.getActionCommand());
			}
			inputs.push(e.getActionCommand());
		}
		
	}
	
	public String calculate() {
		// actually do the calculation
		ArithmeticParser parser = new ArithmeticParser("+", "-", "*", "\u00F7");
		Double result = parser.evaluate(inputs);
		if (result == null) {
			return "<ERROR>";
		}
		if (result.intValue() == result) {
			return String.valueOf(result.intValue());
		}
		DecimalFormat f = new DecimalFormat("##.00");
		f.setMinimumIntegerDigits(1);
		f.setMaximumFractionDigits(14);
		f.setRoundingMode(RoundingMode.HALF_UP);
		String roundedValue = f.format(result.doubleValue());
		return roundedValue;
	}
}