August 24, 2021 deque queue and stack

Deque It's the realization of queue Interface's double ended queue

Deque Usage scenarios of
In general , When concurrency is not involved , There are two implementation classes , It can be selected according to its own characteristics , Namely ：

• LinkedList Variable size linked list double ended queue , Allow elements to be inserted null.
• ArrayDeque Variable size array double ended queue , Inserting... Is not allowed null.
• ConcurrentLinkedDeque Variable size and thread safe linked list double ended queue , Non blocking , Inserting... Is not allowed null.
• LinkedBlockingDeque Thread safe double ended queues , When the queue is empty , Get operation will block , Until an element is added .
  Be careful ：LinkedList and ArrayDeque Is a thread unsafe container .
  Java There is Stack This class , But it is not recommended . Usually use Deque To complete the functions of queue and stack .

Deque It's an interface , In fact, there are ：

• ArrayDeque, Use “ Array ” Store the data
• LinkedList, Use “ Linked list ” Store the data
• ConcurrentLinkedDeque, Thread safe LinkedList

The queue is a typical fifo （FIFO） The container of . That is to put things from one end of the container , Take out... From the other end , And the order in which things are put into the container is the same as the order in which they are taken out .
Two ways to implement queues ：

   1: Deque<String> queue = new LinkedList<String>();
   2: queue.offer("data1");    // Add an element at the end of the queue 
   3: queue.offer("data2");
   4: queue.offer("data3");
   5: System.out.println(queue.poll());    // Get the first element of the team , And delete from the queue 
   6:  
   7: Deque<String> stack = new LinkedList<String>();
   8: stack.push("element1");    // Push the elements towards the top of the stack 
   9: stack.push("element2");
  10: stack.push("element3");
  11: System.out.println(stack.pop());    // Get the top of the stack element , And delete from the top of the stack 

1、offer() and add() The difference between ------------------ The team
add() and offer() It's all about adding an element to the queue . But if you want to add a new element to a full queue , call add() Method will throw a unchecked abnormal , And call offer() Method will return false. According to this, we can make an effective judgment in the program ！

2、peek() and element() The difference between ----------------------- Take the team leader
peek() and element() Will return to the head of the team without removing it , however peek() Method returns... When the queue is empty null, call element() Method will throw NoSuchElementException abnormal .

3、poll() and remove() The difference between ------------------------ Out of the team
poll() and remove() All will be removed and returned to the opposite , But in poll() Returns... When the queue is empty null, and remove() Will throw out NoSuchElementException abnormal .