Bubblesort.java

import java.util.*;

/** Program that sorts an arbitrary array of integers using the bubble sort algorithm.
 * @author Felix Rabe
 * @version 20111024
 */
public class Bubblesort {
    public static final Random random = new Random();
    public static final int TEST_DATA_LENGTH = 20;

    public static void main(String[] args) {
        int[] inputs;
        if (args.length == 0) {
            inputs = generateRandomIntArray();
        } else {
            inputs = stringsToInts(args);
        }
        int[] outputs = inputs.clone();
        sortInPlace(outputs);
        printOut(inputs, outputs);
    }

    private static int[] stringsToInts(String[] strings) {
        int[] ints = new int[strings.length];
        for (int i = 0; i < ints.length; i++) {
            String string = strings[i];
            try {
                ints[i] = Integer.parseInt(string);
            } catch (NumberFormatException e) {
                System.out.println("Is this a number? '" + string + "' - I don't think so!");
                // I chose to keep invalid numbers as 0 in the array.
            }
        }
        return ints;
    }

    private static void printOut(int[] inputs, int[] outputs) {
        System.out.println("    Inputs:     Outputs:");
        for (int i = 0; i < outputs.length; i++) {
            System.out.printf("%12d %12d\n", inputs[i], outputs[i]);
        }
    }

    /** Generate a random array of integers.
     * @return the generated array
     */
    public static int[] generateRandomIntArray() {
        return generateRandomIntArray(TEST_DATA_LENGTH);
    }

    /** Generate a random array of integers.
     * @param length the length of the array to be generated
     * @return the generated array
     */
    public static int[] generateRandomIntArray(int length) {
        int[] randomArray = new int[length];
        for (int i = 0; i < length; i++) {
            randomArray[i] = random.nextInt();
        }
        return randomArray;
    }

    /** Sort the specified integer array in-place.  Uses the bubble sort algorithm.
     * @param array the array to sort
     */
    public static void sortInPlace(int[] array) {
        boolean hadToSwap;
        do {
            hadToSwap = false;
            for (int first = 0; first < array.length - 1; first++) {
                int second = first + 1;
                if (array[first] > array[second]) {
                    swap(array, first, second);
                    hadToSwap = true;
                }
            }
        } while(hadToSwap);
    }

    /** Swap two elements in the given array.
     * @param array the array in which to swap the elements
     * @param first the index of the first element to swap
     * @param second the index of the second element to swap
     */
    private static void swap(int[] array, int first, int second) {
        int tmp = array[first];
        array[first] = array[second];
        array[second] = tmp;
    }
}