Queue and Deque

table of Contents

• Queue

• LinkedList

• PriorityQueue

• and

• ArrayDeque

Queue

(Message Queuing) Queue like queues of people standing in the front can buy go first, into the tail, the head of the queue.

Common methods:

method	Explanation
public boolean add(E e)	Increased data, will throw an exception
public boolean offer(E e)	Increase data return true if successful, will not throw an exception
public E remove()	Delete data, will throw an exception
public E poll()	Deleting data, do not throw an exception

LinkedList

LinkedList is a subclass of Queue.

Example:

public class TestQueue {
    public static void main(String[] args) {
        Queue<String> queue = new LinkedList<>();
        queue.add("1");
        queue.add("2");
        queue.add("4");
        queue.add("5");
        while(!queue.isEmpty()){
            System.out.print("【"+queue.poll()+"】、");
        }
    }
}

result:

【1】、【2】、【4】、【5】、

PriorityQueue

PriorityQueue a priority queue will be output according to the natural order.

Example:

public class TestPriorityQueue {
    public static void main(String[] args) {
        Queue<String> queue = new PriorityQueue<>();
        queue.add("a");
        queue.add("B");
        queue.add("A");
        queue.add("1");
        queue.add("9");
        queue.add("C");
        queue.add("x");
        queue.add("G");
        while(!queue.isEmpty()){
            System.out.print(queue.poll()+"、");
        }
    }
}

result:

1、9、A、B、C、G、a、x、	//根据ASCII码大小进行排序

and

Dqeue Queue is a subclass has the function of two-way queue, you can add data or pop-up data for the first or the tail.

ArrayDeque

Example:

public class TestDeque {
    public static void main(String[] args) {
        Deque<String> deque = new ArrayDeque<>();
        deque.offerFirst("hello");
        deque.offerLast("world");
        deque.offerFirst("2020");
        deque.offerLast("☆☆☆☆☆");
        //返回头部元素
        System.out.println(deque.peekFirst());
        //返回尾部元素
        System.out.println(deque.peekLast());
        while(!deque.isEmpty()){
            //弹出数据
            System.out.print(deque.poll()+"  ");
        }
    }
}

result:

2020
☆☆☆☆☆
2020  hello  world  ☆☆☆☆☆