Merge Sort (Java)

gistfile1.txt

package homeworks;

/**
 *
 * @author Petr
 */
class Homework1 implements Mergesort{


    public int[] getFirstHalfOf(int[] array) {
        if (array.length % 2 != 0) {
            int[] firstHalf = new int[(array.length / 2) + 1];
            System.arraycopy(array, 0, firstHalf, 0, (array.length / 2) + 1);
            return firstHalf;
        } else {
            int[] firstHalf = new int[array.length / 2];
            System.arraycopy(array, 0, firstHalf, 0, array.length / 2);
            return firstHalf;
        }
    }

    public int[] getSecondHalfOf(int[] array) {
        int[] secondHalf = new int[array.length / 2];
        System.arraycopy(array, array.length - array.length / 2, secondHalf, 0, array.length / 2);
        return secondHalf;
    }

    public int[] merge(int[] firstHalf, int[] secondHalf) {  
        int arr1[] = firstHalf;
        int arr2[] = secondHalf;
        int[] helpArr = new int[arr1.length];
        int array[] = new int[firstHalf.length + secondHalf.length];

        int mainArrayIndex = 0, firstArrayIndex = 0, secondArrayIndex = 0;

        while (arr1.length > 0 || arr2.length > 0) {
            if (arr1.length > 0 && arr2.length > 0) {
                if (arr1[0] <= arr2[0]) {
                    array[mainArrayIndex] = arr1[0];
                    helpArr = arr1;
                    arr1 = new int[helpArr.length-1];
                    System.arraycopy(helpArr, 1, arr1, 0, arr1.length);
                    mainArrayIndex++;
                } else {
                    array[mainArrayIndex] = arr2[0];
                    helpArr = arr2;
                    arr2 = new int[helpArr.length-1];
                    System.arraycopy(helpArr, 1, arr2, 0, arr2.length);
                    mainArrayIndex++;
                }
            } else if (arr1.length > 0) {
                array[mainArrayIndex] = arr1[0];
                helpArr = arr1;
                    arr1 = new int[helpArr.length-1];
                    System.arraycopy(helpArr, 1, arr1, 0, arr1.length);
                mainArrayIndex++;

            } else if (arr2.length > 0) {
                array[mainArrayIndex] = arr2[0];
                helpArr = arr2;
                    arr2 = new int[helpArr.length-1];
                    System.arraycopy(helpArr, 1, arr2, 0, arr2.length);
                mainArrayIndex++;
            }
        }
        return array;
    }

    public int[] mergesort(int[] array) {
	if(array.length <= 1){
            return array;
        }
	
		int lengthOfArray1 = array.length/2;
		int elementsInA2 = lengthOfArray1;
		if((array.length % 2) == 1)
			lengthOfArray1 += 1;

		int arr1[] = getFirstHalfOf(array);
		int arr2[] = getSecondHalfOf(array);

                System.arraycopy(array, 0, arr1, 0, arr1.length);
                System.arraycopy(array, arr1.length, arr2, 0, arr2.length);

		arr1 = mergesort(arr1);
		arr2 = mergesort(arr2);

		

        return merge(arr1, arr2);
    }
}
interface Mergesort {
    int[] getFirstHalfOf(int[] array); // vrati nesetridenou kopii prvni poloviny (horni celou cast) pole array
    int[] getSecondHalfOf(int[] array); // vrati nesetridenou kopii druhe poloviny (dolni celou cast) pole array
    int[] merge(int[] firstHalf, int[] secondHalf); // slije prvky v firstHalf a secondHalf do jednoho pole a vrati ho
    int[] mergesort(int[] array); // vrati setridenou kopii pole array
}

class Main {
    public static void main(String[] args) {

        int A[] = new int[10];
        int B[] = {};
        int C[] = {};
        populateArray(A);
        Homework1 homework = new Homework1();
        int D[]=homework.merge(B, C);
        printArray(D);




        System.out.println("Pred razenim:");
        printArray(A);

        A = homework.mergesort(A);

        System.out.println("\nPo razeni: ");
        printArray(A);
        

}
    public static void printArray(int[] array) {
        for (int i = 0; i < array.length; i++) {
            System.out.print(array[i] + " ");
        }
        System.out.println("");
    }

    public static int[] populateArray(int[] array) {
        for (int i = 0; i < array.length; i++) {
            array[i] = (int) (Math.random() * 100);
        }
        return array;
    }
}