Java工具包中的Arrays工具类里面有数组的快速排序算法。
源码如下：
/**
* Sorts the specified range of the array using the given
* workspace array slice if possible for merging
*
* @param a the array to be sorted
* @param left the index of the first element, inclusive, to be sorted
* @param right the index of the last element, inclusive, to be sorted
* @param work a workspace array (slice)
* @param workBase origin of usable space in work array
* @param workLen usable size of work array
*/
static void sort(int[] a, int left, int right,
int[] work, int workBase, int workLen) {
// Use Quicksort on small arrays
if (right - left < QUICKSORT_THRESHOLD) {
sort(a, left, right, true);
return;
} /*
* Index run[i] is the start of i-th run
* (ascending or descending sequence).
*/
int[] run = new int[MAX_RUN_COUNT + 1];
int count = 0; run[0] = left; // Check if the array is nearly sorted
for (int k = left; k < right; run[count] = k) {
if (a[k] < a[k + 1]) { // ascending
while (++k <= right && a[k - 1] <= a[k]);
} else if (a[k] > a[k + 1]) { // descending
while (++k <= right && a[k - 1] >= a[k]);
for (int lo = run[count] - 1, hi = k; ++lo < --hi; ) {
int t = a[lo]; a[lo] = a[hi]; a[hi] = t;
}
} else { // equal
for (int m = MAX_RUN_LENGTH; ++k <= right && a[k - 1] == a[k]; ) {
if (--m == 0) {
sort(a, left, right, true);
return;
}
}
} /*
* The array is not highly structured,
* use Quicksort instead of merge sort.
*/
if (++count == MAX_RUN_COUNT) {
sort(a, left, right, true);
return;
}
} // Check special cases
// Implementation note: variable "right" is increased by 1.
if (run[count] == right++) { // The last run contains one element
run[++count] = right;
} else if (count == 1) { // The array is already sorted
return;
} // Determine alternation base for merge
byte odd = 0;
for (int n = 1; (n <<= 1) < count; odd ^= 1); // Use or create temporary array b for merging
int[] b; // temp array; alternates with a
int ao, bo; // array offsets from 'left'
int blen = right - left; // space needed for b
if (work == null || workLen < blen || workBase + blen > work.length) {
work = new int[blen];
workBase = 0;
}
if (odd == 0) {
System.arraycopy(a, left, work, workBase, blen);
b = a;
bo = 0;
a = work;
ao = workBase - left;
} else {
b = work;
ao = 0;
bo = workBase - left;
} // Merging
for (int last; count > 1; count = last) {
for (int k = (last = 0) + 2; k <= count; k += 2) {
int hi = run[k], mi = run[k - 1];
for (int i = run[k - 2], p = i, q = mi; i < hi; ++i) {
if (q >= hi || p < mi && a[p + ao] <= a[q + ao]) {
b[i + bo] = a[p++ + ao];
} else {
b[i + bo] = a[q++ + ao];
}
}
run[++last] = hi;
}
if ((count & 1) != 0) {
for (int i = right, lo = run[count - 1]; --i >= lo;
b[i + bo] = a[i + ao]
);
run[++last] = right;
}
int[] t = a; a = b; b = t;
int o = ao; ao = bo; bo = o;
}
}
java.util.Arrays类能方便的操作数组，它所有的方法都是静态的。
1.filll方法 ：给数组中的某段元素附上相同值。
2.sort方法：对数组中某段元素排序。
3.equals方法：比较两个数组，判断的是数组中元素值是否相等。
4.binarySearch方法：对排过序的数组进行二分法查找。
测试用例：
package recursion; import java.util.Arrays; /**
* @author zsh
* @company wlgzs
* @create 2019-02-17 9:33
* @Describe Arrays方法测试
*/
public class TestForArrays { public static void main(String[] args) {
//填充数组，将arr[]中所有元素的值初始为0
int[] arr = new int[5];
Arrays.fill(arr,12);
System.out.println(Arrays.toString(arr));
//将arr中的第2个到第三个元素的值赋为8
Arrays.fill(arr,1,3,8);
System.out.println(Arrays.toString(arr));
//对数组进行排序
int[] arr1 = new int[]{7,6,8,5,2,9,8,1,3,5};
//对数组的第二个到第6个元素进行排序
Arrays.sort(arr1,1,6);
System.out.println(Arrays.toString(arr1));
//对整个数组进行排序
Arrays.sort(arr1);
System.out.println(Arrays.toString(arr1));
//比较数组元素是否相等
System.out.println(Arrays.equals(arr,arr1));
//使用二分法在数组中查找指定元素所在的下标
//数组必须是先排好序的
System.out.println(Arrays.binarySearch(arr1,5));
//如果不存在，就返回负数
System.out.println(Arrays.binarySearch(arr1,20));
} }
控制台输出：
