A simple calculator.

Calculator.java

package calculator;

import java.util.Scanner;

/**
 * Calculator
 * A class that offers simple calculator functionality.
 * 
 * @author Matthew Sullivan
 */
public class Calculator {
    
    /**
     * @param args the argument strings
     */
    public static void main(String[] args) {
        double total = 0.00;
        double lastNumber = 0.00;
        Scanner console = new Scanner(System.in); // my input
        
        /**
         * Be a polite calculator.
         */
        System.out.println("This is a simple calculator. Enter a number followed by the operator on a new line.");
        try {
            lastNumber = Integer.parseInt(console.next()); // get the first line
        } catch(Exception e) {
            lastNumber = Double.parseDouble(console.next()); // again, but if it's a double
        }
        while(!console.nextLine().equals("stop")) { // allow an exit like a gentleman
            String line = console.next(); // assign the line variable
            switch(line) {
                case "+":
                    total += lastNumber; // add to the total
                    break;
                case "-":
                    total -= lastNumber; // or subtract
                    break;
                case "*":
                    total *= lastNumber; // or multiply
                    break;
                case "/":
                    if(lastNumber != 0) {
                        total /= lastNumber; // or divide
                    } else {
                        System.out.println("If you divide by zero the universe implodes, so how about not.");
                    }
                    break;
                case "=":
                    System.out.println(total); // tell us the grand total!
                    break;
                default:
                    try {
                        lastNumber = Integer.parseInt(line); // look for an int to assign
                    } catch(Exception e) {
                        lastNumber = Double.parseDouble(line); // look for a double
                    }
            }
        }
    }
}