用队列实现栈

import java.util.ArrayDeque;

/**
 * 用队列实现栈
 */
public class QueueToStack {

    public static class Mystack<T> {

        // 此处把ArrayDeque当做队列使用
        public ArrayDeque<T> data;

        public ArrayDeque<T> help;

        public int size;

        public Mystack() {
            data = new ArrayDeque();
            help = new ArrayDeque();
        }

        public void push(T value) {
            if (help.isEmpty()) {
                data.push(value);
            } else {
                help.push(value);
            }
            size++;
        }

        public T pop() {
            if (isEmpty()) {
                System.out.println("the statck is empty");
                return null;
            }
            size--;
            if (data.isEmpty()) {
                for (int i = 0; i < size; i++) {
                    data.push(help.pollLast());
                }
                return help.pollLast();
            } else {
                for (int i = 0; i < size; i++) {
                    help.push(data.pollLast());
                }
                return data.pollLast();
            }
        }

        public boolean isEmpty() {
            return size == 0;
        }

    }

}

/* 如有错误，欢迎批评指正 */