廢話不說，直接上程式碼

package com.search;

public class SearchOfMid {

	public static void main(String[] args) {
		int [] arr = {1,3,4,5,2,5,1,8,9,5};
		//常規方式
		System.out.println(find(arr,9));
		//遞迴實現
		System.out.println(recursiveFind(arr,0,arr.length-1,9));
	}
	/*
	 * 二分查詢，返回索引
	 */
	private static int find(int [] arr,int searchKey){
            int lowerBound = 0;
            int upperBound = arr.length -1;
            int curIn;
            while(lowerBound <= upperBound){
                curIn = (lowerBound + upperBound) / 2;
                if(arr[curIn] == searchKey){
                    return curIn;
                }else{
                    if(arr[curIn] < searchKey){
                        lowerBound = curIn + 1;
                    }else{
                        upperBound = curIn - 1;
                    }
                }
            }
            return -1;
        }
	/*
	 * 二分查詢，返回索引，遞迴實現
	 */
	private static int recursiveFind(int[] arr,int start,int end,int searchKey){
            if (start <= end) {
                int middle =  (start+end)/2;
                if (searchKey == arr[middle]) {
                    return middle;
                } else if (searchKey < arr[middle]) {
                    return recursiveFind(arr, start, middle - 1, searchKey);
                } else {
                    return recursiveFind(arr, middle + 1, end, searchKey);
                }
            } else {
                return -1;
            }
        }      
}