Stack simulation queue

The characteristic of the stack ： Last in, first out （Last In First Out）

The characteristics of the queue are ： fifo （First In First Out）

         The idea of simulating queues with stacks ： First define two stacks in and out, With the stack in To store elements , Stack out To output elements , Press into the stack in order when entering the team in in , From the stack in Pop up and press into the stack out in , According to the characteristics of stack , Stack in order out Just get the elements out of the stack . The specific implementation is as follows ：

public static void main(String[] args) {
		MyQueue<String> queue = new MyQueue<String>();
		queue.offer("A1");
		queue.offer("A2");
		queue.offer("A3");
		queue.offer("A4");
		queue.offer("A5");
		System.out.println(queue.poll() + " Out of the team ");

		//  Traverse 
		while (!queue.isEmpty()) {
			System.out.println(queue.poll());
		}
	}
}

// Use stack to simulate queue 
class MyQueue<E> {
	private Stack<E> in = new Stack<E>(); //  Join the team 
	private Stack<E> out = new Stack<E>(); //  Out of the stack 

	//  The team 
	public void offer(E e) {
		while (!out.isEmpty()) {
			in.push(out.pop());
		}
		in.push(e);
	}

	public boolean isEmpty() {

		return in.size() == 0 && out.size() == 0;
	}

	//  Out of the team 
	public E poll() {
		while (!in.isEmpty()) {
			out.push(in.pop());
		}
		return out.pop();
	}

Be careful ： Make sure to stack when joining the team out There's no element in it , That is, put them all on the stack in in , When leaving the team, you should also ensure that the stack in There are no elements in it , That is, all out of the team ！！