Analysis of the difference between queues (Queue) and lists (List) in Java

The difference between queues (queues) and lists (lists) in Java

In Java, queues and lists are two commonly used data structures, which are used in different scenarios respectively. Although they can all store a set of elements, there are significant differences in how, characteristics and applicable scenarios. This article will explore the differences between queues and lists in detail and help readers understand when to use them.

1. Basic concepts

1.1 List

Lists are a data structure in the Java collection framework that allows the storage of ordered collections of elements. Elements in the list can be accessed through the index and repeat elements are allowed. Common list implementation classes includeArrayListandLinkedList。

• Orderful: The elements in the list are ordered and can be accessed through the index.
• Repeat allowed: List allows storing duplicate elements.
• Random access: Lists support quick access to elements through indexes.

1.2 Queue

A queue is a first-in-first-out (FIFO, First In First Out) data structure that is usually used to process elements that need to be processed sequentially. Elements in the queue can only be added from the end of the team and removed from the head of the team. Common queue implementation classes includeLinkedList、PriorityQueueandArrayDeque。

• First in first out: The queue follows the FIFO principle, and the elements that enter the queue are first removed.
• Operation restricted: Queues usually only allow elements to be added at the end of the queue and elements to be removed at the head of the queue.
• Random access is not allowed: Queue does not support accessing elements through indexes.

2. Main differences

2.1 Data structure characteristics

• List: List is an ordered collection that allows access to elements through indexes and supports random access. Elements in the list can be repeated and can be inserted anywhere.
• Queue: A queue is a first-in-first-out data structure, and elements can only be added from the end of the team and removed from the head of the team. Queues do not support random access and generally do not allow insertion or removal of elements in the middle.

2.2 Operation method

List：

• Add elements:add(E e)、add(int index, E element)
• Delete elements:remove(int index)、remove(Object o)
• Get elements:get(int index)
• Modify elements:set(int index, E element)

Queue：

• Add elements:offer(E e)、add(E e)
• Remove elements:poll()、remove()
• Check out the team head elements:peek()、element()
• Queues do not support accessing or modifying elements through indexes.

2.3 Applicable scenarios

List：

• Use lists when an ordered set of elements needs to be stored and elements need to be accessed frequently through indexes.
• Use lists when you need to insert or delete elements anywhere.
• Use list when elements are allowed to be repeated.

Queue：

• Use queues when elements need to be processed in first-in-first-out order.
• When you need to implement task scheduling, message delivery and other scenarios, use queues.
• Use queues when it is necessary to limit the processing order of elements.

3. Code example

3.1 List example

import ;
import ;
public class ListExample {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>();
        ("Apple");
        ("Banana");
        ("Cherry");
        // Access elements through index        ("First element: " + (0));
        // Modify elements        (1, "Blueberry");
        // Delete elements        (2);
        // traverse the list        for (String fruit : list) {
            (fruit);
        }
    }
}

3.2 Queue Example

import ;
import ;
public class QueueExample {
    public static void main(String[] args) {
        Queue<String> queue = new LinkedList<>();
        ("Apple");
        ("Banana");
        ("Cherry");
        // Check the team head elements        ("First element: " + ());
        // Remove the head element        ();
        // traverse the queue        while (!()) {
            (());
        }
    }
}

4. Summary

• ListSuitable for scenarios where orderly storage, random access, and allowing duplicate elements.
• QueueSuitable for scenarios where elements need to be processed in first-in-first-out order.

In actual development, choosing the right data structure can significantly improve the efficiency and readability of the code. Understanding the difference between queues and lists can help developers make the right choices in different scenarios.

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