TestBubbleSort2.java

public class TestBubbleSort2 {

    /**
    *   Program:    TestBubbleSort2.java
    *   Purpose:    Test running time of bubble sort with sorted versus unsorted arrays.
    *   Creator:    Chris Clarke
    *   Created:    05.02.2015
    */

    static final int MAX=100000; // a hundred thousand

    public static int[] initSortedArray() {
        int[] theArray = new int[MAX];
        for (int i=0; i<theArray.length; i++) {
            theArray[i] = i;
        } // for

        return theArray;
    } // initSortedArray()

    public static int[] getShuffledArray(int min, int max) {

        /**
        *   max is the array size
        *   when min=0, range is 0 to max-1
        *   shuffle or rearrange the array values
        */

        int[] theArray, results;
        theArray = new int[max];
        results = new int[max];

        int r;  // a random number

        // initialise the array
        for (int i=0; i<max; i++)
            theArray[i]=i+min; // when min=1, range is 1 to max inclusive
                       // when min=0, range is 0 to max-1 inclusive

        // pick n numbers
        for (int i=0; i<max; i++) {
            // range 1 to 49, 1 to 48 etc
            r = (int) ((max-i) * Math.random());
            // store results
            results[i] = theArray[r];
            // move last number in theArray to position r
            theArray[r] = theArray[max-1-i];
        } // end for

        return results;

    } // end getShuffledArray()


    public static int[] sort(int[] a) {
    // apply bubblesort algorithm to array a
        int i, j, temp;
        int len = a.length;
        boolean swaps; // optimise code: when no swaps, array is sorted

        for (i=0; i<len-1; i++) {
            swaps = false;
            for (j=0; j<len-1-i; j++) {
                if (a[j]>a[j+1]) {
                    // swap
                    temp=a[j];
                    a[j]=a[j+1];
                    a[j+1]=temp;
                    swaps = true;
                } // if
            } // for j
            if (!swaps) break; // from outer loop
        } // for i

        return a;
    } // sort()

    public static void main(String[] args) {
        NanoTimer timer = new NanoTimer();
        int[] sorted = initSortedArray();
        int[] unsorted = getShuffledArray(0, MAX);
        System.out.println("Array size: "+sorted.length);
        System.out.println("Sorting sorted array...");
        timer.setStartTime();
        sorted = sort(sorted);
        timer.setStopTime();
        System.out.println("Sorted.  Running time: "+timer.toString());
        System.out.println("Sorting unsorted array...");
        timer.setStartTime();
        sorted = sort(unsorted);
        timer.setStopTime();
        System.out.println("Sorted.  Running time: "+timer.toString());
    } // main()

} // class TestBubbleSort2

class NanoTimer {

    /**
    *   Class:      NanoTimer.java
    *   Purpose:    Get program running times in nanoseconds
    *   Creator:    Chris Clarke
    *   Created:    03.04.2014
    */

    private long startTime = 0, runningTime = -1;

    public void setStartTime() {
        startTime = System.nanoTime();
    }

    public void setStopTime() {
        runningTime = System.nanoTime() - startTime;
    }

    public String toString() {
        if (runningTime == -1)
            return "Error in running time.";

        return runningTime+" nanoseconds";
    }

} // class NanoTimer