public boolean containsKey(Object key) {
        return getEntry(key) != null;
    }
Returns <tt>true</tt> if this map contains a mapping for the specified
key.

@param key
           The key whose presence in this map is to be tested
@return <tt>true</tt> if this map contains a mapping for the specified
        key.
src/main/java/com/alibaba/fastjson/util/AntiCollisionHashMap.java