// 栈 先进后出
Stack<Integer> stack = new Stack<>();
stack.push(1);
stack.push(2);
System.out.println(stack.pop());
System.out.println(stack.pop());
// 队列 先进先出
Queue<Integer> queue = new LinkedList<>();
queue.add(1);
queue.add(2);
System.out.println(queue.remove());
System.out.println(queue.remove());