Queue

queue: FIFO,

Queue is interface, the implementation could be LinkedList or array

offer, poll, peek, size() isEmpty()

public static void main(String[] args){
    Queue<Integer> queue = new LinkedList<>() ;
    System.out.println(queue.size()); //0: empty queue size = 0
    queue.offer(5);
    queue.offer(3);
    System.out.println(queue.size()); //2
    System.out.println(queue.poll()); //5
    System.out.println(queue.peek()); //3
    System.out.println(queue.isEmpty()); //false
    System.out.println(queue.poll()); //3
    System.out.println(queue.isEmpty()); //true
}