java实现二分查找

public int BinarySearch（int[] a, int key）{
int  beginIndex=0;
int  endIndex=a.length-1;
int midIndex=0;
while(a!==null&&beginIndex<endIndex){
midIndex=(beginIndex+endIndex)/2;
if(midIndex==key) return midIndex;
else if(midIndex<key) beginIndex=midIndex+1;
else endIndex=midIndex-1;
}
return -1;
}

public int BinarySearch(int[] a , int key , int beginIndex, int endIndex){
int midIndex=(beginIndex+endIndex)/2;
if(a==null||beginIndex<endIndex||key<a[beginIndex]) return -1;
else if(a[midIndex]==key) return midIndex;
else if(a[midIndex]>key) return BinarySearch(a,key,beginIndex,midIndex-1);
else  return BinarySearch(a,key,midIndex+1,endIndex);
}