Java中的 ConcurrentLinkedQueue 示例

Java中的ConcurrentLinkedQueue类是Java集合框架的一部分。它属于Java.util.concurrent包。它是在 JDK 1.5 中引入的。它用于在 LinkedList 的帮助下同时实现 Queue。它是 Queue 的无界线程安全实现，它以 FIFO（先进先出）的方式在 Queue 的尾部插入元素。它可以在多个线程之间共享无界队列时使用。此类不允许空元素。迭代器是弱一致的。此类及其迭代器实现了Queue和Iterator接口的所有可选方法。
类层次结构：

java.lang.Object
  ↳ java.util.AbstractCollection
     ↳ java.util.AbstractQueue
        ↳ Class ConcurrentLinkedQueue

宣言：

public class ConcurrentLinkedQueue extends AbstractCollection implements Queue, Serializable 
 

这里， E是这个集合维护的元素的类型。

ConcurrentLinkedQueue 的构造函数

要构造 ConcurrentLinkedQueue，我们需要从Java.util.ConcurrentLinkedQueue导入它。

1. ConcurrentLinkedQueue() ：该构造函数用于构造一个空队列。

ConcurrentLinkedQueue clq = new ConcurrentLinkedQueue();

2. ConcurrentLinkedQueue(Collection c) ：该构造函数用于构造一个队列，将 Collection 的元素作为参数传递。

ConcurrentLinkedQueue clq = new ConcurrentLinkedQueue(Collection c);

下面是一个示例程序，用于说明Java中的 ConcurrentLinkedQueue：

示例 1：

Java

// Java program to demonstrate ConcurrentLinkedQueue
 
import java.util.concurrent.*;
 
class ConcurrentLinkedQueueDemo {
   
    public static void main(String[] args)
    {
        // Create a ConcurrentLinkedQueue
        // using ConcurrentLinkedQueue() constructor
        ConcurrentLinkedQueue
            clq = new ConcurrentLinkedQueue();
 
        clq.add(12);
        clq.add(70);
        clq.add(1009);
        clq.add(475);
 
        // Displaying the existing LinkedQueue
        System.out.println("ConcurrentLinkedQueue: "
                           + clq);
 
        // Create a ConcurrentLinkedQueue
        // using ConcurrentLinkedQueue(Collection c)
        // constructor
        ConcurrentLinkedQueue
            clq1 = new ConcurrentLinkedQueue(clq);
 
        // Displaying the existing LinkedQueue
        System.out.println("ConcurrentLinkedQueue1: "
                           + clq1);
    }
}

输出：

ConcurrentLinkedQueue: [12, 70, 1009, 475]
ConcurrentLinkedQueue1: [12, 70, 1009, 475]

示例 2：

Java

// Java code to illustrate
// methods of ConcurrentLinkedQueue
 
import java.util.concurrent.*;
 
class ConcurrentLinkedQueueDemo {
   
    public static void main(String[] args)
    {
 
        // Create a ConcurrentLinkedQueue
        // using ConcurrentLinkedQueue()
          // constructor
        ConcurrentLinkedQueue
            clq = new ConcurrentLinkedQueue();
 
        clq.add(12);
        clq.add(70);
        clq.add(1009);
        clq.add(475);
 
        // Displaying the existing ConcurrentLinkedQueue
        System.out.println("ConcurrentLinkedQueue: "
                           + clq);
 
        // Displaying the first element
        // using peek() method
        System.out.println("First Element is: "
                           + clq.peek());
 
        // Remove and display the first element
        // using poll() method
        System.out.println("Head Element is: "
                           + clq.poll());
 
        // Displaying the existing ConcurrentLinkedQueue
        System.out.println("ConcurrentLinkedQueue: "
                           + clq);
 
        // Get the size using size() method
        System.out.println("Size: "
                           + clq.size());
    }
}

输出：

ConcurrentLinkedQueue: [12, 70, 1009, 475]
First Element is: 12
Head Element is: 12
ConcurrentLinkedQueue: [70, 1009, 475]
Size: 3

基本操作

1.添加元素

ConcurrentLinkedQueue 提供了两种添加元素的方法。

• add() 它插入元素，作为参数传递到这个 ConcurrentLinkedQueue 的尾部。如果插入成功，此方法返回 True。 ConcurrentLinkedQueue 是无界的，所以这个方法永远不会抛出 IllegalStateException 或返回 false。
• addAll() 它插入集合的所有元素，在 ConcurrentLinkedQueue 的末尾作为参数传递。元素的插入与集合的迭代器返回的顺序相同。

Java

// Java Program Demonstrate adding
// elements to ConcurrentLinkedQueue
 
import java.util.concurrent.*;
import java.util.*;
 
public class AddingElementsExample {
   
    public static void main(String[] args)
    {
 
        // Create an instance of ConcurrentLinkedQueue
        ConcurrentLinkedQueue queue = new ConcurrentLinkedQueue();
 
        // Add String to queue using add method
        queue.add("Kolkata");
        queue.add("Patna");
        queue.add("Delhi");
        queue.add("Jammu");
 
        // Displaying the existing ConcurrentLinkedQueue
        System.out.println("ConcurrentLinkedQueue: " + queue);
 
        // create a ArrayList of Strings
        ArrayList arraylist = new ArrayList();
   
        // add String to ArrayList
        arraylist.add("Sanjeet");
        arraylist.add("Rabi");
        arraylist.add("Debasis");
        arraylist.add("Raunak");
        arraylist.add("Mahesh");
 
        // Displaying the existing Collection
        System.out.println("Collection to be added: " + arraylist);
 
        // apply addAll() method and passed
        // the arraylist as parameter
        boolean response = queue.addAll(arraylist);
 
        // Displaying the existing ConcurrentLinkedQueue
        System.out.println("Collection added: " + response);
 
        // Displaying the existing ConcurrentLinkedQueue
        System.out.println("ConcurrentLinkedQueue: " + queue);
    }
}

输出

ConcurrentLinkedQueue: [Kolkata, Patna, Delhi, Jammu]
Collection to be added: [Sanjeet, Rabi, Debasis, Raunak, Mahesh]
Collection added: true
ConcurrentLinkedQueue: [Kolkata, Patna, Delhi, Jammu, Sanjeet, Rabi, Debasis, Raunak, Mahesh]

2. 移除元素

ConcurrentLinkedQueue 的 remove(Object o) 方法用于删除指定元素的单个实例（如果存在）。它删除一个元素e ，使得 o.equals(e)。如果此 ConcurrentLinkedQueue 包含指定的元素，则返回 true，否则返回 false。

Java

// Java Program Demonstrate removing
// elements from ConcurrentLinkedQueue
 
import java.util.concurrent.*;
 
public class RemovingElementsExample {
   
    public static void main(String[] args)
    {
 
        // Create an instance of ConcurrentLinkedQueue
        ConcurrentLinkedQueue queue = new ConcurrentLinkedQueue();
 
        // Add Numbers to queue using add(e) method
        queue.add(4353);
        queue.add(7824);
        queue.add(78249);
        queue.add(8724);
 
        // Displaying the existing ConcurrentLinkedQueue
        System.out.println("ConcurrentLinkedQueue: " + queue);
 
        // apply remove() for Number 78249
        boolean response = queue.remove(78249);
 
        // print results
        System.out.println("Removing Number 78249 successful: " + response);
 
        // Displaying the existing ConcurrentLinkedQueue
        System.out.println("Updated ConcurrentLinkedQueue: " + queue);
    }
}

输出

ConcurrentLinkedQueue: [4353, 7824, 78249, 8724]
Removing Number 78249 successful: true
Updated ConcurrentLinkedQueue: [4353, 7824, 8724]

3. 迭代元素

ConcurrentLinkedQueue 的 iterator() 方法用于以适当的顺序返回与此 ConcurrentLinkedQueue 相同元素的迭代器。此方法返回的元素包含从 first(head) 到 last(tail) 顺序的元素。返回的迭代器是弱一致的。

Java

// Java Program Demonstrate Iterating
// over ConcurrentLinkedQueue
 
import java.util.concurrent.*;
import java.util.*;
 
public class TraversingExample {
   
    public static void main(String[] args)
    {
        // Create an instance of ConcurrentLinkedQueue
        ConcurrentLinkedQueue queue = new ConcurrentLinkedQueue();
 
        // Add String to queue using add(e) method
        queue.add("Aman");
        queue.add("Amar");
        queue.add("Sanjeet");
        queue.add("Rabi");
 
        // Displaying the existing ConcurrentLinkedQueue
        System.out.println("ConcurrentLinkedQueue : " + queue);
 
        // Call iterator() method
        Iterator iterator = queue.iterator();
 
        // Print elements of iterator
        System.out.println("\nThe String Values of iterator are:");
        while (iterator.hasNext()) {
            System.out.println(iterator.next());
        }
    }
}

输出

ConcurrentLinkedQueue : [Aman, Amar, Sanjeet, Rabi]

The String Values of iterator are:
Aman
Amar
Sanjeet
Rabi

4. 访问元素

Queue提供的 peek() 和 element() 方法用于访问 ConcurrentLinkedQueue 的元素。

element()方法与peek( ) 方法的不同之处仅在于如果此队列为空，它将引发异常。

Java

// Java Program Demonstrate accessing
// elements of ConcurrentLinkedQueue
 
import java.util.*;
import java.util.concurrent.*;
 
public class AccessingElementsExample {
   
    public static void main(String[] args) throws IllegalStateException
    {
        // Create an instance of ConcurrentLinkedQueue
        ConcurrentLinkedQueue Q = new ConcurrentLinkedQueue<>();
 
        // Add numbers to end of Queue
        Q.add(7855642);
        Q.add(35658786);
        Q.add(5278367);
        Q.add(74381793);
 
        // print queue
        System.out.println("Queue: " + Q);
 
        // print head
        System.out.println("Queue's head: " + Q.element());
 
        // print head
        System.out.println("Queue's head: " + Q.peek());
    }
}

输出

Queue: [7855642, 35658786, 5278367, 74381793]
Queue's head: 7855642
Queue's head: 7855642

ConcurrentLinkedQueue 的方法

METHOD	DESCRIPTION
add​(E e)	Inserts the specified element at the tail of this queue.
addAll​(Collection c)	Appends all of the elements in the specified collection to the end of this queue, in the order that they are returned by the specified collection’s iterator.
contains​(Object o)	Returns true if this queue contains the specified element.
forEach​(Consumer action)	Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception.
isEmpty()	Returns true if this queue contains no elements.
iterator()	Returns an iterator over the elements in this queue in the proper sequence.
offer​(E e)	Inserts the specified element at the tail of this queue.
remove​(Object o)	Removes a single instance of the specified element from this queue, if it is present.
removeAll​(Collection c)	Removes all of this collection’s elements that are also contained in the specified collection (optional operation).
removeIf​(Predicate filter)	Removes all of the elements of this collection that satisfy the given predicate.
retainAll​(Collection c)	Retains only the elements in this collection that are contained in the specified collection (optional operation).
size()	Returns the number of elements in this queue.
spliterator()	Returns a Spliterator over the elements in this queue.
toArray()	Returns an array containing all of the elements in this queue, in the proper sequence.
toArray​(T[] a)	Returns an array containing all of the elements in this queue, in proper sequence; the runtime type of the returned array is that of the specified array.

在类Java.util.AbstractQueue 中声明的方法

METHOD	DESCRIPTION
clear()	Removes all the elements from this queue.
element()	Retrieves, but does not remove, the head of this queue.
remove()	Retrieves and removes the head of this queue.

在类Java.util.AbstractCollection 中声明的方法

METHOD	DESCRIPTION
containsAll​(Collection c)	Returns true if this collection contains all of the elements in the specified collection.
toString()	Returns a string representation of this collection.

在接口Java.util.Collection 中声明的方法

METHOD	DESCRIPTION
clear()	Removes all of the elements from this collection (optional operation).
containsAll​(Collection c)	Returns true if this collection contains all of the elements in the specified collection.
equals​(Object o)	Compares the specified object with this collection for equality.
hashCode()	Returns the hash code value for this collection.
parallelStream()	Returns a possibly parallel Stream with this collection as its source.
stream()	Returns a sequential Stream with this collection as its source.
toArray​(IntFunction generator)	Returns an array containing all of the elements in this collection, using the provided generator function to allocate the returned array.

在接口Java .util.Queue 中声明的方法

METHOD	DESCRIPTION
element()	Retrieves, but does not remove, the head of this queue.
peek()	Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.
poll()	Retrieves and removes the head of this queue, or returns null if this queue is empty.
remove()	Retrieves and removes the head of this queue.

参考： Java : Java