请问java中sort 大数据的含义
代码为：
private static void sort1(int x[], int off, int len) {
// Insertion sort on smallest arrays
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
int m = off + (len > > 1); // Small arrays, middle element
if (len > 7) {
int l = off;
int n = off + len - 1;
if (len > 40) { // Big arrays, pseudomedian of 9
int s = len/8;
l = med3(x, l, l+s, l+2*s);//特别是这个部分，//到底是要找什么值啊
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
}
int v = x[m];

// 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 middle
int 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-elements
if ((s = b-a) > 1)
sort1(x, off, s);
if ((s = d-c) > 1)
sort1(x, n-s, s);
}
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);
}

private static void swap(int x[], int a, int b) {
int t = x[a];
x[a] = x[b];
x[b] = t;
}

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));
}


[解决办法]
其实就算为了防止快排退化。
分别在前面，中间，后面各取3个数的中位数，然后再取总的3个数的中位数。使得快排时的分割尽量平衡。