Java-二分查找算法

package com.lym.binarySearch;

import java.util.Arrays;

/**
* 二分查找
*
* @author Administrator
*
*/
public class BinarySearchDemo {

public static void main(String[] args) {
int[] number = { 4, 2, 66, 12, 88, 95, 63, 1 };
Arrays.sort(number);// 先对数组排序，然后再进行二分查找
int index = binarySearch(number, 63);//parameter(int[],key)
System.out.println(index);
}

//二分查找
public static int binarySearch(int[] a, int n) {
rangeCheck(a.length,0,a.length-1);
return binarySearch0(a, 0, a.length, n);
}

//异常检测
private static void rangeCheck(int length, int fromIndex, int toIndex) {
if (fromIndex > toIndex) {
throw new IllegalArgumentException(
"fromIndex(" + fromIndex + ") > toIndex(" + toIndex + ")");
}
if (fromIndex < 0) {
throw new ArrayIndexOutOfBoundsException(fromIndex);
}
if (toIndex > length) {
throw new ArrayIndexOutOfBoundsException(toIndex);
}
}

//二分查找核心算法
private static int binarySearch0(int[] a, int fromIndex, int toIndex, int n) {
int low = fromIndex;
int high = toIndex - 1;

while (low <= high) {
int mid = (low + high) >>> 1;// middle index    采用移位运算符可以提高性能
int midVal = a[mid];// middle value

if (midVal > n)
high = mid - 1;
else if (midVal < n)
low = mid + 1;
else
return mid;//key found
}
return -(low + 1);// key no found
}

}