divide by 0 exception

[Randall Twede]

i wrote a calculator program like the windows one(well sort of). anyway i had to add a lot of if's to catch bad input that would result in a runtime exception. now i think i am down to only having the divide by 0 one left. if you can find others please let me know. anyway i cant just say if text.equals("0") because it could also be "0.0" ...hmm i could OR them hmmm..

i plan to refactor it when i shake all the bugs out im just wondering if any of you can find some more exception throwing code. or code that doesn't perform correctly.

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

public class Calculator
{
    private JFrame frame = new JFrame();
	private JTextField display = new JTextField();
	private JPanel mainPanel = new JPanel();
    private JPanel buttonPanel = new JPanel();
	private JPanel topPanel = new JPanel();
	private JPanel centerPanel = new JPanel();
	private JPanel westPanel = new JPanel();
	private JTextField memoryFlag = new JTextField();
	private JButton backspace = new JButton("Backspace");
	private JButton ce = new JButton("CE");
	private JButton c = new JButton("C");
	private JButton mc = new JButton("MC");
	private JButton mr = new JButton("MR");
	private JButton ms = new JButton("MS");
	private JButton mPlus = new JButton("M+");
	private JButton seven = new JButton("7");
	private JButton eight = new JButton("8");
	private JButton nine = new JButton("9");
	private JButton divide = new JButton("/");
	private JButton sqrt = new JButton("sqrt");
	private JButton four = new JButton("4");
	private JButton five = new JButton("5");
	private JButton six = new JButton("6");
	private JButton multiply = new JButton("*");
	private JButton mod = new JButton("%");
	private JButton one = new JButton("1");
	private JButton two = new JButton("2");
	private JButton three = new JButton("3");
	private JButton minus = new JButton("-");
	private JButton fraction = new JButton("1/x");
	private JButton zero = new JButton("0");
	private JButton sign = new JButton("+/-");
	private JButton decimal = new JButton(".");
	private JButton plus = new JButton("+");
	private JButton equals = new JButton("=");
	private ButtonListener listener = new ButtonListener();
	private double operandA;
	private double operandB;
	private String operator;
	private Double result;
	private boolean isNegative = false;
	private String memory = "";
	//private JMenuBar menuBar = new JMenuBar();

    /** Creates a new instance of Calculator */
    public Calculator()
    {
		frame.setSize(400, 300);
		frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setTitle("Calculator");
		initComponents();
        Container c = frame.getContentPane();
		c.setLayout(new BorderLayout());
		c.add(display, "North");
		c.add(mainPanel, "Center");
		//frame.setJMenuBar(menuBar);
		frame.setVisible(true);
		
	}

    // improves the readability of the constructor	
	private void initComponents()
	{
		memoryFlag.setEditable(false);
		display.setHorizontalAlignment(JTextField.TRAILING);
		buttonPanel.setLayout(new BorderLayout());
		topPanel.setLayout(new GridLayout(1,3,5,5));
		backspace.addActionListener(listener);
		topPanel.add(backspace);
		ce.addActionListener(listener);
		topPanel.add(ce);
		c.addActionListener(listener);
		topPanel.add(c);
		centerPanel.setLayout(new GridLayout(4,5,5,5));
		seven.addActionListener(listener);
		centerPanel.add(seven);
		eight.addActionListener(listener);
		centerPanel.add(eight);
		nine.addActionListener(listener);
		centerPanel.add(nine);
		divide.addActionListener(listener);
		centerPanel.add(divide);
		sqrt.addActionListener(listener);
		centerPanel.add(sqrt);
		four.addActionListener(listener);
		centerPanel.add(four);
		five.addActionListener(listener);
		centerPanel.add(five);
		six.addActionListener(listener);
		centerPanel.add(six);
		multiply.addActionListener(listener);
		centerPanel.add(multiply);
		mod.addActionListener(listener);
		centerPanel.add(mod);
		one.addActionListener(listener);
		centerPanel.add(one);
		two.addActionListener(listener);
		centerPanel.add(two);
		three.addActionListener(listener);
		centerPanel.add(three);
		minus.addActionListener(listener);
		centerPanel.add(minus);
		fraction.addActionListener(listener);
		centerPanel.add(fraction);
		zero.addActionListener(listener);
		centerPanel.add(zero);
		sign.addActionListener(listener);
		centerPanel.add(sign);
		decimal.addActionListener(listener);
		centerPanel.add(decimal);
		plus.addActionListener(listener);
		centerPanel.add(plus);
		equals.addActionListener(listener);
		centerPanel.add(equals);
		westPanel.setLayout(new GridLayout(5,1,5,5));
		westPanel.add(memoryFlag);
		mc.addActionListener(listener);
		westPanel.add(mc);
		mr.addActionListener(listener);
		westPanel.add(mr);
		ms.addActionListener(listener);
		westPanel.add(ms);
		mPlus.addActionListener(listener);
		westPanel.add(mPlus);
		buttonPanel.add(topPanel, "North");
		buttonPanel.add(centerPanel, "Center");
		mainPanel.setLayout(new BorderLayout());
		mainPanel.add(westPanel, "West");
		mainPanel.add(buttonPanel, "Center");
	}

	private void binary()
	{
		switch(operator)
		{
			case "+":
				result = new Double(operandA + operandB);
				display.setText(result.toString());
				break;
			case "-":
				result = new Double(operandA - operandB);
				display.setText(result.toString());
				break;
			case "*":
				result = new Double(operandA * operandB);
				display.setText(result.toString());
				break;
			case "/":
				result = new Double(operandA / operandB);
				display.setText(result.toString());
				break;
			case "%":
				result = new Double(operandA % operandB);
				display.setText(result.toString());
				break;
		}
	}
	
	class ButtonListener implements ActionListener
	{
		public void actionPerformed(ActionEvent e)
		{
			String button = e.getActionCommand();
			String text = display.getText();
			switch(button)
			{
				//numeric
				case "0":
				case "1":
				case "2":
				case "3":
				case "4":
				case "5":
				case "6":
				case "7":
				case "8":
				case "9":
				case ".":
					display.setText(text + button);
					break;
				//binary
				case "+":
					if(!text.equals(""))
					{
						operandA = Double.parseDouble(text);
						operator = "+";
						display.setText("");
					}
					break;
				case "-":
					if(!text.equals(""))
					{
						operandA = Double.parseDouble(text);
						operator = "-";
						display.setText("");
					}
					break;
				case "*":
					if(!text.equals(""))
					{
						operandA = Double.parseDouble(text);
						operator = "*";
						display.setText("");
					}
					break;
				case "/":
					if(!text.equals(""))
					{
						operandA = Double.parseDouble(text);
						operator = "/";
						display.setText("");
					}
					break;
				case "%":
					if(!text.equals(""))
					{
						operandA = Double.parseDouble(text);
						operator = "%";
						display.setText("");
					}
					break;
				case "=":
					if(!text.equals(""))
					{
						operandB = Double.parseDouble(text);
						binary();
					}
					break;
				//unary
				case "1/x":
					if(!text.equals(""))
					{
						operandA = Double.parseDouble(text);
						result = new Double(1 / operandA);
						display.setText(result.toString());
					}
					break;
				case "sqrt":
					if(!text.equals(""))
					{
						operandA = Double.parseDouble(text);
						result = new Double(Math.sqrt(operandA));
						display.setText(result.toString());
					}
					break;
				//memory
				case "MC":
					memory = "";
					memoryFlag.setText("");
					break;
				case "MR":
					display.setText(memory);
					break;
				case "MS":
					memory = text;
					memoryFlag.setText("M");
					display.setText("");
					break;
				case "M+":
					if(!text.equals(""))
					{
						Double sum = new Double(Double.parseDouble(memory) + Double.parseDouble(text));
						memory = sum.toString();
						display.setText("");
					}
					break;
				//misc
				case "C":
                                        operandA = 0;
                                        operation = "";
				case "CE":
					display.setText("");
					break;
				case "Backspace":
					if(!text.equals(""))
					{
						display.setText(text.substring(0, (text.length() - 1)));
					}
					break;
				case "+/-":
					if(!text.equals(""))
					{
						if(isNegative)
						{
							display.setText(text.substring(1, text.length()));
						}
						else
						{
							display.setText("-" + text);
						}
						isNegative = isNegative ? false : true;
					}
					break;
			}	//end switch
		}		//end actonPerformed()			
	}			//end ButtonListener
	
    // create and display an instance of Calculator
    public static void main(String args[])
    {  
        SwingUtilities.invokeLater(new Runnable()
		{  
            public void run()
			{  
				new Calculator();  
      	    }  
		});
    }
}

[Campbell Ritchie]

I would suggest you refactor your Listener class, too. That single method is far too long. Individual Listeners associated with each button would be better. You could have a NumberListener class with 0, 1, 2 etc., as fields for the individual instances.

What about creating a BigDecimal instance from the text, testing its difference from ZERO with the compareTo method and throwing the Exception if the difference is 0?

[Randall Twede]

i like the single switch statement to handle all action events. it is thanks to java7 that i can do it so easily. i forgot to mention you need java7 to compile or run this.

i was thinking along the same lines. i was going to use Double.parseDouble() to change it to a number and then compare. if they are trying to divide by zero i will use JOptionPane to alert them.....BigDecimal and ZERO look better

i am going to add two lines of code to my original post(rather than repost it all) the case "C" block