Arrays中的sort算法

下面是java.util.Arrays中sort算法的源码，这里以对int数组排序的算法为例，分析一下jdk源码中的排序算法

 

  public static void sort(int[] a) {sort1(a, 0, a.length); } private static void sort1(int x[], int off, int len) {// 对于小数组进行归并排序if (len < 7) { for (int i=off; i<len+off; i++)for (int j=i; j>off && x[j-1]>x[j]; j--) swap(x, j, j-1); return;}// Choose a partition element, v //这里的主要目的是当数组比较大是用快速排序法进行排序，为了防止快速排序的退化，取一个恰当的中位数，作为快速排序的理想中值，使快速排序效率提高。int m = off + (len >> 1); // Small arrays, middle elementif (len > 7) { int l = off; int n = off + len - 1; if (len > 40) { // Big arrays, pseudomedian of 9int s = len/8;l = med3(x, l, l+s, l+2*s);m = med3(x, m-s, m, m+s);n = med3(x, n-2*s, n-s, n); } m = med3(x, l, m, n); // Mid-size, med of 3} //取得的中值int v = x[m]; //快速排序// Establish Invariant: v* (<v)* (>v)* v*int a = off, b = a, c = off + len - 1, d = c;while(true) { while (b <= c && x[b] <= v) {if (x[b] == v) swap(x, a++, b);b++; } while (c >= b && x[c] >= v) {if (x[c] == v) swap(x, c, d--);c--; } if (b > c)break; swap(x, b++, c--);}// Swap partition elements back to middleint s, n = off + len;s = Math.min(a-off, b-a ); vecswap(x, off, b-s, s);s = Math.min(d-c, n-d-1); vecswap(x, b, n-s, s);// Recursively sort non-partition-elementsif ((s = b-a) > 1) sort1(x, off, s);if ((s = d-c) > 1) sort1(x, n-s, s); } /** * Swaps x[a] with x[b]. * 交换 x[a] 和x[b] */ private static void swap(int x[], int a, int b) {int t = x[a];x[a] = x[b];x[b] = t; } /** * Swaps x[a .. (a+n-1)] with x[b .. (b+n-1)]. * 交换 x[a .. (a+n-10] 和 x[b .. (b+n-1)] */ private static void vecswap(int x[], int a, int b, int n) {for (int i=0; i<n; i++, a++, b++) swap(x, a, b); } /** * Returns the index of the median of the three indexed integers. * 返回三个int类型的中值 */ private static int med3(int x[], int a, int b, int c) {return (x[a] < x[b] ?(x[b] < x[c] ? b : x[a] < x[c] ? c : a) :(x[b] > x[c] ? b : x[a] > x[c] ? c : a)); }