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Pax Wicket Service is an OSGi extension of the Wicket framework, allowing for dynamic loading and unloading of Wicket components and pageSources.

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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.
 */
package org.apache.wicket.util.watch;

import java.util.Set;

import org.apache.wicket.util.listener.IChangeListener;
import org.apache.wicket.util.time.Duration;


/**
 * Monitors one or more IModifiable objects, calling a {@link IChangeListener
 * IChangeListener} when a given object's modification time changes.
 * 
 * @author Juergen Donnerstag
 */
public interface IModificationWatcher
{
	/**
	 * Adds an IModifiable object and an IChangeListener object to call
	 * when the modifiable object is modified.
	 * 
	 * @param modifiable
	 *            an IModifiable object to monitor
	 * @param listener
	 *            an IChangeListener to call if the IModifiable object is
	 *            modified
	 * @return true if the set did not already contain the specified element
	 */
	boolean add(final IModifiable modifiable, final IChangeListener listener);

	/**
	 * Removes all entries associated with an IModifiable object.
	 * 
	 * @param modifiable
	 *            an IModifiable object
	 * @return the IModifiable object that was removed, else null
	 */
	IModifiable remove(final IModifiable modifiable);

	/**
	 * Starts watching at a given Duration polling rate.
	 * 
	 * @param pollFrequency
	 *            the polling rate Duration
	 */
	void start(final Duration pollFrequency);

	/**
	 * Stops this ModificationWatcher.
	 */
	void destroy();

	/**
	 * Retrieves a key set of all IModifiable objects currently being monitored.
	 * 
	 * @return a Set of all IModifiable entries currently maintained
	 */
	Set getEntries();
}