Concurrent Stack

ConcurrentStack.java

/**
 * Description: Concurrent Stack
 *
 * @author liuzhengyang
 * @version 1.0
 * @since 2016-04-07
 */
public class ConcurrentStack<E> {
	private AtomicReference<Node<E>> top = new AtomicReference<>();

	public void push(E item) {
		Node<E> newHead = new Node<>(item);
		Node<E> old = null;
		do {
			old = top.get();
			newHead.next = old;
		} while(!(top.compareAndSet(old, newHead)));
	}

	public E pop() {
		Node<E> oldHead;
		Node<E> newHead;
		do {
			oldHead = top.get();
			if (oldHead == null) {
				return null;
			}
			newHead = oldHead.next;
		} while (!(top.compareAndSet(oldHead, newHead)));
		return oldHead.item;
	}

	public boolean isEmpty() {
		return top.get() == null;
	}

	public E peek() {
		if (top.get() == null) {
			return null;
		} else {
			return top.get().item;
		}
	}

	private static class Node<E> {
		private E item;
		private Node<E> next;

		public Node(E item) {
			this.item = item;
		}
	}
}