Java中Collections.sort()排序方法举例详解

 public static void main(String[] args) {
    Integer[] nums = new Integer[]{3, 7, 9, 2, 1};
    Arrays.sort(nums, new Comparator<Integer>() {
        @Override
        public int compare(Integer o1, Integer o2) {
            return o1 - o2;
        }
    });
    for (Integer i : nums) {
        System.out.print(i + "  ");  // 1 2 3 7 9
    }
}

public static void main(String[] args) {
    Integer[] nums = new Integer[]{3, 7, 9, 2, 1};
    Arrays.sort(nums, new Comparator<Integer>() {
        @Override
        public int compare(Integer o1, Integer o2) {
            return o2 - o1;
        }
    });
    for (Integer i : nums) {
        System.out.print(i + "  ");9 7 3 2 1
    }
}

public static <T> void sort(T[] a, Comparator<? super T> c) {
    if (c == null) {
        sort(a);
    } else {
        if (LegacyMergeSort.userRequested)
            legacyMergeSort(a, c);
        else
            TimSort.sort(a, 0, a.length, c, null, 0, 0);
    }
}

private static <T> void legacyMergeSort(T[] a, Comparator<? super T> c) {
    T[] aux = a.clone();
    if (c==null)
        mergeSort(aux, a, 0, a.length, 0);
    else
        mergeSort(aux, a, 0, a.length, 0, c);
}

private static void mergeSort(Object[] src,Object[] dest,int low, int high, int off,Comparator c) {
        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 && c.compare(dest[j-1], 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, c);
        mergeSort(dest, src, mid, high, -off, c);
        // 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 (c.compare(src[mid-1], 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 && c.compare(src[p], src[q]) <= 0)
                dest[i] = src[p++];
            else
                dest[i] = src[q++];
        }
    }

if (length < INSERTIONSORT_THRESHOLD) {
    for (int i=low; i<high; i++)
        for (int j=i; j>low && c.compare(dest[j-1], dest[j])>0; j--)
            swap(dest, j, j-1);
    return;
}