java jdk中的归并排序实现

在Arrays.java中的sort中 ?

    public static void sort(Object[] a, int fromIndex, int toIndex) {        if (LegacyMergeSort.userRequested)            legacyMergeSort(a, fromIndex, toIndex);        else            ComparableTimSort.sort(a, fromIndex, toIndex);    }    /** To be removed in a future release. */    private static void legacyMergeSort(Object[] a,                                        int fromIndex, int toIndex) {        rangeCheck(a.length, fromIndex, toIndex);        Object[] aux = copyOfRange(a, fromIndex, toIndex);        mergeSort(aux, a, fromIndex, toIndex, -fromIndex);    }    /**     * Tuning parameter: list size at or below which insertion sort will be     * used in preference to mergesort.     * To be removed in a future release.     */    private static final int INSERTIONSORT_THRESHOLD = 7;    /**     * Src is the source array that starts at index 0     * Dest is the (possibly larger) array destination with a possible offset     * low is the index in dest to start sorting     * high is the end index in dest to end sorting     * off is the offset to generate corresponding low, high in src     * To be removed in a future release.     */    private static void mergeSort(Object[] src,                                  Object[] dest,                                  int low,                                  int high,                                  int off) {        int length = high - low;        // Insertion sort on smallest arrays        if (length < INSERTIONSORT_THRESHOLD) {            for (int i=low; i<high; i++)                for (int j=i; j>low &&                         ((Comparable) dest[j-1]).compareTo(dest[j])>0; j--)                    swap(dest, j, j-1);            return;        }        // Recursively sort halves of dest into src        int destLow  = low;        int destHigh = high;        low  += off;        high += off;        int mid = (low + high) >>> 1;        mergeSort(dest, src, low, mid, -off);        mergeSort(dest, src, mid, high, -off);        // If list is already sorted, just copy from src to dest.  This is an        // optimization that results in faster sorts for nearly ordered lists.        if (((Comparable)src[mid-1]).compareTo(src[mid]) <= 0) {            System.arraycopy(src, low, dest, destLow, length);            return;        }        // Merge sorted halves (now in src) into dest        for(int i = destLow, p = low, q = mid; i < destHigh; i++) {            if (q >= high || p < mid && ((Comparable)src[p]).compareTo(src[q])<=0)                dest[i] = src[p++];            else                dest[i] = src[q++];        }    }