Java实现一个二分查找

import java.util.*;

public class BinarySearch {
    public int getPos(int[] A, int n, int val) {

        int position=-1; //返回的数组的位置
        int low=0,high=n-1,mid=n/2; 
        if(n<=0||A==null){// 数组为空或者为null
             position=-1;
        }else{// 数组有元素
        while(low<=high){
            if(val>A[mid]){
                low=mid+1;
                mid=(low+high)/2;
            }else if(val<A[mid]){
                high=mid-1;
                mid=(low+high)/2;
            }else{
                position=mid;
                break ; //跳出循环
            }
        }
        }
          // 判断position
         if(position==-1)
             return position;
        else{
            while(position>=0&&A[position]==val){
                position--;
            }
            return position+1;
        }
    }
}