question: public void delete ( @ NonNull Key key ) { final ReentrantReadWriteLock . WriteLock lock = guard . writeLock ( ) ; lock . lock ( ) ; try { if ( ! readKeys . remove ( key ) ) throw new IllegalArgumentException ( "key does not exist" ) ; Files . delete ( key . getFile ( ) ) ; } catch ( IOException ex ) { LOG . log ( Level . WARNING , "unable to remove file " + key . getFile ( ) , ex ) ; } finally { lock . unlock ( ) ; } }
target:  Removes the file associated with the given key.