question: public static void clear ( ) { long lock_stamp = lock . writeLock ( ) ; try { idToString = new ArrayList < > ( ) ; stringToId = new HashMap < > ( ) ; idToString . add ( UNKNOWN_ID , UNKNOWN_WORD ) ; stringToId . put ( UNKNOWN_WORD , UNKNOWN_ID ) ; } finally { lock . unlockWrite ( lock_stamp ) ; } }
target:  Clears the vocabulary and initializes it with an unknown word. Registered language models are left unchanged.