code: @Override
  	public boolean contains(final Object value) {
  		lock.readLock().lock();
  		try {
  			if (value == null) {
  				return false;
  			}
  			for (@SuppressWarnings("rawtypes")
  			final Map.Entry entry : entrySet()) {
  				final Object otherValue = entry.getValue();
  				if (otherValue != null && otherValue.equals(value)) {
  					return true;
  				}
  			}
  			return false;
  		} finally {
  			lock.readLock().unlock();
  		}
  	}
docs: /*
  (non-Javadoc)
  
  @see java.util.Hashtable#contains(java.lang.Object)