@Override
    public K getKey() {
      return key;
    }
Binary search for a given key
@param needle The key to look for in all of the entries
@return Same return value as Arrays.binarySearch. Positive numbers mean the index. Otherwise
        (-1 * insertion point) - 1
hbase-common/src/main/java/org/apache/hadoop/hbase/types/CopyOnWriteArrayMap.java