多线程归并排序的实现 java

1.这段代码很简单，就是一个基本的归并排序，知道这个类中的sort实现归并排序就OK.
package 归并排序;

import java.util.Arrays;
public class SequentialMergeSort  {

  
    public void sort(int[] arr) {

        // handle null inputs
        if (arr == null) {
            throw new IllegalArgumentException("Input array cannot be null");
        }

        if (arr.length == 0 || arr.length == 1) {
            // already sorted return
            return;
        }

        int start = 0;
        int end = arr.length - 1;
        mergeSort(arr, start, end);
    }

    // helper method for merge sort
    protected void mergeSort(int[] arr, int start, int end) {
        if (start < end) {
            int mid = (start + end) / 2;
            mergeSort(arr, start, mid);
            mergeSort(arr, mid + 1, end);
            merge(arr, start, mid, end);
        }
    }

    protected void merge(int[] arr, int start, int mid, int end) {

        // copy the left half into left array
        int[] leftArray = Arrays.copyOfRange(arr, start, mid + 1);
        // copy right half into right array
        int[] rightArray = Arrays.copyOfRange(arr, mid + 1, end + 1);
        int leftArrayPtr = 0, rightArrayPtr = 0, inputArrayPtr = start;
        // merge until we reach end of either one of the arrays
        for (; leftArrayPtr < leftArray.length && rightArrayPtr < rightArray.length; inputArrayPtr++) {

            if (leftArray[leftArrayPtr] <= rightArray[rightArrayPtr]) {
                arr[inputArrayPtr] = leftArray[leftArrayPtr];
                leftArrayPtr++;
            } else {
                arr[inputArrayPtr] = rightArray[rightArrayPtr];
                rightArrayPtr++;
            }
        }

        // finish up if there are any remaining elements
        for (; leftArrayPtr < leftArray.length; leftArrayPtr++, inputArrayPtr++) {
            arr[inputArrayPtr] = leftArray[leftArrayPtr];
        }
        for (; rightArrayPtr < rightArray.length; rightArrayPtr++, inputArrayPtr++) {
            arr[inputArrayPtr] = rightArray[rightArrayPtr];
        }
    }

}