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- /*
- * 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.
- */
-
- /* $Id$ */
-
- 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);
-
- }
-
- }
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