public static void main(String[] args) {
	// TODO Auto-generated method stub
	//1 2 3 4 5 6 7 8 9
	int [] a = {1,2,3,4,5,6,7,8,9};
	System.out.println(bsearch(a,6));
}

public static int bsearch (int [] a,int key){
	  	int low = 0;
	    int high = a.length - 1;//8
	    while (low <= high) {
	        int mid = low + (high - low) / 2;
	        if (a[mid] > key)
	            high = mid;//没有所谓的减一
	        else if (a[mid] < key)
	            low = mid;/没有所谓的加一
	        else
	            return mid;
	    }
	    return -1;
}