Interpretation of the usage of commonly used queues in Java

The use of commonly used queues in Java

In Java programming, queues are a very important data structure and are widely used in scenarios such as task scheduling, messaging, and multi-threaded communication.

The following will introduce several commonly used Java queues and their usage methods in detail.

1. Queue interface overview

QueueIt is an interface in the Java collection framework that defines the first-in-first-out (FIFO) data structure behavior. Common implementation classes include:

• LinkedList: Implements a double-ended queue (Deque), which supports insertion and removal operations on both ends.
• ArrayDeque: An efficient queue implementation based on arrays, and also supports dual-ended operations.
• PriorityQueue: A queue sorted by element priorities.

2. Common queue implementation classes and usage

(1) LinkedList as Queue

AlthoughLinkedListMainly used for list structure, but it also implementsQueueInterfaces can be used as queues.

Main methods：

• add(E element): Insert the specified element into the tail of the queue.
• remove(): Removes and returns the header element. If the queue is empty, throwNoSuchElementException。
• peek(): Check the team head elements and do not remove them. If the queue is empty, returnnull。

Sample code：

Queue<String> queue = new LinkedList<>();
("A");
("B");

(()); // Output A
String element = ();
(element); // Output A

(2) ArrayDeque

ArrayDequeIt is an array-based double-ended queue that supports quick insertion and removal of elements on both ends. It implementsQueueandDequeinterface.

Main methods：

• addFirst(E element): Adds the specified element to the queue header.
• addLast(E element): Adds the specified element to the end of the queue.
• removeFirst(): Removes and returns the element at the head of the queue.
• removeLast(): Removes and returns the element at the end of the queue.

Sample code：

Queue<String> deque = new ArrayDeque<>();

("A");
("B");

(()); // Output A
("C"); // Add to header(()); // Output C
String element = (); // Remove the head element C(element); // Output C

(3) PriorityQueue

PriorityQueueis a priority queue in which elements are sorted according to their natural order or specified comparator. The highest priority element is always returned every time it is removed.

Main methods：

• add(E element): Insert the specified element into the queue.
• remove(): Removes and returns the header element (i.e. the element with the highest priority).
• peek(): Check the team head elements and do not remove them.

Sample code：

Queue<Integer> priorityQueue = new PriorityQueue<>();

(3);
(1);
(2);

(()); // Output 1
int element = ();
(element); // Output 1

(4) BlockingQueue

BlockingQueueIt is an interface in Java concurrency package, mainly used in the producer-consumer mode in a multi-threaded environment. Common implementation classes include:

• LinkedBlockingQueue: Bounded or unbounded queues based on linked lists.
• ArrayBlockingQueue: Bounded queue based on array.
• PriorityBlockingQueue: Supports priority bounded queues.

Sample code (using LinkedBlockingQueue)：

import ;

public class BlockingQueueExample {
    public static void main(String[] args) throws InterruptedException {
        BlockingQueue<String> blockingQueue = new LinkedBlockingQueue<>(2);
        
        // Producer thread        Thread producerThread = new Thread(() -> {
            try {
                ("Producers start production...");
                ("Item 1");
                ("Item 2");
                ("Item 3"); // The queue is full, blocking until there is space            } catch (InterruptedException e) {
                ().interrupt();
                ("Producer thread is interrupted...");
            }
        });
        
        // Consumer thread        Thread consumerThread = new Thread(() -> {
            try {
                ("Consumers start to consume...");
                while (true) {
                    String item = ();
                    ("Consumed: " + item);
                }
            } catch (InterruptedException e) {
                ().interrupt();
                ("The consumer thread is interrupted...");
            }
        });
        
        ();
        ();
    }
}

3. Things to note

• Capacity control：
• For bounded queues (e.g.ArrayBlockingQueue), the initial capacity needs to be set reasonably to avoid frequent capacity expansion operations.
• Thread safety：
• BlockingQueueThe implementation classes are thread-safe and are suitable for task distribution and message delivery in multi-threaded environments.
• Performance considerations：
• The performance of different queue implementation classes in insertion, deletion and other operations may be different. For example,ArrayDequeCompare the operation on both endsLinkedListMore efficient.

Summarize

Java provides a variety of queue implementations, each with its applicable scenarios:

• If you need a simple first-in first-out behavior, you can chooseLinkedListorArrayDeque。
• If you need to process according to element priority, you can usePriorityQueue。
• In multi-threaded environment, it is recommended to useBlockingQueueand its subclasses to simplify the complexity of task distribution and synchronization.

By rationally selecting and using these queue structures, the efficiency and maintainability of the code can be significantly improved in actual development.

The above is personal experience. I hope you can give you a reference and I hope you can support me more.