栈和队列的实际实现

双向链表实现

public class MyQueue<T> {
	private Node<T> head;
	private Node<T> tail;
		
	public void push(T value) {
		Node<T> node = new Node(value);
		if (head == null) {
			head = node;
			tail = node;
		} else {
			node.next = head;
			head.prev = node;
			head = node;
		}
	}
	
	public T pop() {
		if (head == null)
			return null;
		Node node = tail;
		if (head == tail) {
			head = null;
			tail = null;
		} else {
			tail = tail.prev;
			node.prev = null;
			tail.next = next;
		}
		return node.value;
	}
	
	public Boolean isEmpty() {
		return head == null;
	}
}

数组实现

public class MyQueue {
	private int pushIndex = 0;
	private int popIndex = 0;
	private int size = 0;
	private int limit = 0;
	private final int[] arr;

	public MyQueue(int limit) {
		arr = new int[limit];
		pushIndex = 0;
		popIndex = 0;
		size = 0;
		this.limit = limit;
	}
		
	public void push(int value) {
		if (size == limit) {
			throw new RuntimeException("不能再添加了！");
		}
		size++;
		arr[pushIndex] = value;
		pushIndex = nextIndex(pushIndex);
	}
	
	public int pop() {
		if (size == 0) {
			throw new RuntimeException("不能再弹出了！");
		}
		size--;
		int value = arr[popIndex];
		popIndex = nextIndex(popIndex);
		return value;
	}
	
	public Boolean isEmpty() {
		return size == 0;
	}
	
	private int nextIndex(int index) {
		return index == limit - 1 ? 0 : index + 1;
	}
}