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
	}

}