org.apache.fop.layoutmgr.ElementListObserver Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/* $Id: ElementListObserver.java 1761021 2016-09-16 11:40:57Z ssteiner $ */
package org.apache.fop.layoutmgr;
import java.util.List;
/**
* This class is used to observe Knuth element lists generated within the layout managers. This
* is mainly used for the purpose of automated testing. This implementation here does nothing.
* Please see the subclass within the test code.
*/
public final class ElementListObserver {
private ElementListObserver() {
}
private static List activeObservers;
/**
* Adds a new Observer to the list.
* @param observer the observer implementation
*/
public static void addObserver(Observer observer) {
if (!isObservationActive()) {
activeObservers = new java.util.ArrayList();
}
activeObservers.add(observer);
}
/**
* Removes an Observer from the list. This call simply returns if the observer was not on
* the list and does nothing.
* @param observer the observer to remove
*/
public static void removeObserver(Observer observer) {
if (isObservationActive()) {
activeObservers.remove(observer);
}
}
/**
* Notifies all registered observers about the element list.
* @param elementList the Knuth element list
* @param category the category for the element list (example: main, static-content, table-cell)
* @param id ID for the element list (may be null)
*/
public static void observe(List elementList, String category, String id) {
if (isObservationActive()) {
if (category == null) {
throw new NullPointerException("category must not be null");
}
for (Object activeObserver : activeObservers) {
((Observer) activeObserver).observe(elementList, category, id);
}
}
}
/** @return true if observation is active, i.e. Observers are registered. */
public static boolean isObservationActive() {
return activeObservers != null;
}
/**
* Implement this interface to receive notifications on element lists.
*/
public interface Observer {
/**
* Notifies the observer about the element list.
* @param elementList the Knuth element list
* @param category the category for the element list (example: main, static-content or
* table-cell)
* @param id ID for the element list (may be null)
*/
void observe(List elementList, String category, String id);
}
}