Arrays.binarySearch() 的用法

1.binarySearch(Object[] a, Object key)

Searches the specified array for the specified object using the binary search algorithm.

参数1：a是要查询的数组；参数2：key是要查询的关键字；返回值是key所在数组的索引值，如果没有找到就返回-1

注意：该数组必须是升序排列的

2.查看具体源代码：

private static int binarySearch0(Object[] a, int fromIndex, int toIndex,

Object key) {

int low = fromIndex;

int high = toIndex - 1;

while (low <= high) {

int mid = (low + high) >>> 1;

Comparable midVal = (Comparable)a[mid];

int cmp = midVal.compareTo(key);

if (cmp < 0)

low = mid + 1;

else if (cmp > 0)

high = mid - 1;

else

return mid; // key found

}

return -(low + 1); // key not found.

}

3.自己写例子使用

import java.util.Random;

public class Test {

public static void main(String[] args) {

Object[] a = new Object[1000];

for(int i=0;i<a.length;i++){

Integer myint = i+1;

a[i]=myint;

}

Integer key = new Random().nextInt(a.length);

int keyindex = mybinarySearch0(a,0,a.length,key);

if(keyindex>=0)

System.out.println("找到的key："+a[keyindex]);

}

private static int mybinarySearch0(Object[] a, int fromIndex, int toIndex,

Object key) {

int low = fromIndex;

int high = toIndex - 1;

//这也是为什么数组必须升序排列的

while (low <= high) {

//>>> 无符号右移,高位补0，这里相当于/2

int mid = (low + high) >>> 1;

Comparable midVal = (Comparable) a[mid];