用队列实现栈

import java.util.ArrayDeque;
import java.util.Queue;

public class StackByQueue {
    private Queue<Integer> inQueue;
    private Queue<Integer> outQueue;
    private Queue<Integer> tempQueue = null;

    /**
     * Initialize your data structure here.
     */
    public StackByQueue() {
        this.inQueue = new ArrayDeque<>();
        this.outQueue = new ArrayDeque<>();
    }


    /**
     * Push element x onto stack.
     */
    public void push(int x) {
        inQueue.offer(x);
        while (!outQueue.isEmpty()) {
            inQueue.offer(outQueue.poll());
        }
        tempQueue = inQueue;
        inQueue = outQueue;
        outQueue = tempQueue;

    }

    /**
     * Removes the element on top of the stack and returns that element.
     */
    public int pop() {
        return outQueue.poll();
    }

    /**
     * Get the top element.
     */
    public int top() {
        return outQueue.peek();
    }

    /**
     * Returns whether the stack is empty.
     */
    public boolean empty() {
        return outQueue.isEmpty();
    }


    public static void main(String[] args) {
        StackByQueue obj = new StackByQueue();
        obj.push(1);
        obj.push(2);

        int param_2 = obj.pop();
        int param_3 = obj.top();
        boolean param_4 = obj.empty();
    }

}