MergeSort.java

package Sorts;

import static Sorts.SortUtils.print;

/**
 * This method implements the Generic Merge Sort
 *
 *
 * @author Varun Upadhyay (https://github.com/varunu28)
 * @author Podshivalov Nikita (https://github.com/nikitap492)
 *
 *
 * @see SortAlgorithm
 *
 */

class MergeSort implements SortAlgorithm {


    /**
     * This method implements the Generic Merge Sort
     * @param unsorted the array which should be sorted
     * @param <T> Comparable class
     * @return sorted array
     */
    @Override
    @SuppressWarnings("unchecked")
    public <T extends Comparable<T>> T[] sort(T[] unsorted) {
        T[] tmp = (T[]) new Comparable[unsorted.length];
        doSort(unsorted, tmp, 0, unsorted.length - 1);
        return unsorted;
    }

    /**
     *
     * @param arr The array to be sorted
     * @param temp The copy of the actual array
     * @param left The first index of the array
     * @param right The last index of the array
     * Recursively sorts the array in increasing order
     **/
    private  static <T extends Comparable<T>> void doSort(T[] arr, T[] temp, int left, int right) {
        if (left < right) {
            int mid = left + (right - left) / 2;
            doSort(arr, temp, left, mid);
            doSort(arr,  temp,mid + 1, right);
            merge(arr, temp, left, mid, right);
        }

    }

    /**
     * This method implements the merge step of the merge sort
     *
     * @param arr The array to be sorted
     * @param temp The copy of the actual array
     * @param left The first index of the array
     * @param mid The middle index of the array
     * @param right The last index of the array
     * merges two parts of an array in increasing order
     **/

    private static <T extends Comparable<T>> void merge(T[] arr, T[] temp, int left, int mid, int right) {
        System.arraycopy(arr, left, temp, left, right - left + 1);


        int i= left;
        int j = mid + 1;
        int k = left;

        while (i <= mid && j <= right) {
            if (temp[i].compareTo(temp[j]) <= 0) {
                arr[k++] = temp[i++];
            }
            else {
                arr[k++] = temp[j++];
            }
        }

        while (i <= mid) {
            arr[k++] = temp[i++];
        }

	while (j <= right) {
	    arr[k++] = temp[j++];
	}
    }

    // Driver program
    public static void main(String[] args) {

        // Integer Input
        Integer[] arr = {4, 23, 6, 78, 1, 54, 231, 9, 12};
        MergeSort mergeSort = new MergeSort();
        mergeSort.sort(arr);

        // Output => 1	   4  	 6	9	12	23	54	78	231
        print(arr);

        // String Inpu
        String[] stringArray = {"c", "a", "e", "b","d"};
        mergeSort.sort(stringArray);
        //Output => a	b	c	d	e
        print(stringArray);
    }
}