public boolean containsKey(Object key) {
        int hashCode = hash((key == null) ? NULL : key);
        HashEntry entry = data[hashIndex(hashCode, data.length)]; // no local for hash index
        while (entry != null) {
            if (entry.hashCode == hashCode && isEqualKey(key, entry.getKey())) {
                return true;
            }
            entry = entry.next;
        }
        return false;
    }
Checks whether the map contains the specified key.

@param key the key to search for
@return true if the map contains the key
jphp-runtime/src/php/runtime/common/collections/map/AbstractHashedMap.java