JAVA二分查找

package cn.sdut;

public class mm {
    public static int binary_search(int a[],int key)
    {
        int l = 0;
        int r = a.length-1;
        int mid=0;
        while(l<=r)
        {
            mid=(r-l)/2+l;
            if(key>a[mid])
            {
                l=mid+1;
            }
            else if(key<a[mid])
            {
                r=mid-1;
            }
            else return mid;
        }
        if(l>r)
            return -1;
        return mid;
    }
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        int a[]={2,4,7,9,34,67,89,121};
        int key=7;
        int result=mm.binary_search(a, key);
        System.out.println(result);
    }

}