JAVA二分递归查找算法

package part1;
/**
 * 先排序后查找
 * 二分查找，递归实现
 * @author R
 *
 */
public class BinarySearch {
  public static void main(String args[]){
	  int[] a={1,2,3,4,5,6,7,8,9,10,11};
	  
	  int key=rank(3,a);
	  System.out.println(key);
  }
  public static int rank(int key,int a[]){
	  return rank(key,a,0,a.length-1);
  }
  public static int rank(int key,int a[],int lo,int hi){
	  if( lo > hi) return -1;//error
	  int mid = lo + (hi-lo)/2;
	  if( key < a[mid] ) return rank(key,a ,lo , mid-1);
	  else if (key > a[mid] ) return rank(key ,a ,mid+1,hi);
	  else return mid;
  }
}