CurrentElementCounter.java

/*******************************************************************************
 * Copyright 2011 André Rouél
 * 
 * Licensed 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 net.sf.jacclog.util.observer;

import java.util.Queue;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * A thread-safe observer for an <code>ObservableQueue</code> to count the current number of elements stored in a queue.
 * 
 * @author André Rouél
 */
public class CurrentElementCounter<E> implements QueueItemCounter<E> {

	private final AtomicInteger counter = new AtomicInteger();

	@Override
	public void added(final Queue<E> queue, final E element) {
		if (element != null) {
			counter.incrementAndGet();
		}
	}

	@Override
	public void empty(final Queue<E> queue) {
		// not interesting, do nothing
	}

	@Override
	public int getCount() {
		return counter.get();
	}

	@Override
	public void removed(final Queue<E> queue, final E element) {
		if (element != null) {
			counter.decrementAndGet();
		}
	}

}