question: private void checkState ( final boolean usesMiddles ) throws IllegalStateException { if ( beginnings == null ) { throw new IllegalStateException ( "The list of beginnings is null." ) ; } if ( usesMiddles && middles == null ) { throw new IllegalStateException ( "The list of middles is null." ) ; } if ( endings == null ) { throw new IllegalStateException ( "The list of endings is null." ) ; } if ( beginnings . size ( ) == 0 ) { throw new IllegalStateException ( "The list of beginnings is empty." ) ; } if ( usesMiddles && middles . size ( ) == 0 ) { throw new IllegalStateException ( "The list of middles is empty." ) ; } if ( endings . size ( ) == 0 ) { throw new IllegalStateException ( "The list of endings is empty." ) ; } }
target:  Checks the current state of the builder for any issue with it's state. If no issue is found, then no exception is thrown.