public void enter(Object monitor){
  if (monitor == null) {
    throw new NullPointerException();
  }
  monitors.add(monitor);
}

public void enter ( Object monitor ) { if ( monitor == null ) { throw new NullPointerException ( ) ; } monitors . add ( monitor ) ; }
do not use - - for internal use only . < p > should be called after a monitorenter instruction has been executed . tracks the object that monitorenter was used on .
