Java ConcurrentLinkedQueue retainAll() method

The retainAll() method of ConcurrentLinkedQueue class keeps only those elements in this queue that are present in the defined collection.

Syntax:

Specified By:

The retainAll() method of ConcurrentLinkedQueue class is specified by :

retainAll() method in interface Collection<E>.

Override:

The retainAll() method of ConcurrentLinkedQueue class is overrided by:

retainAll() method in class AbstractCollection<E>.

Parameters:

c - The collection contains the elements which is to be kept in this collection.

Return Value:

The retainAll() method returns true if this collection changes as a result of the call.

Throws:

The retainAll() method throws NullPointerException if this collection contains one or more null elements.

Example 1

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ConcurrentLinkedQueue;
public class ConcurrentLinkedQueueRetainAllExample1 {
    public static void main(String[] args) throws InterruptedException {
        List<Integer> list = new ArrayList<Integer>();
        ConcurrentLinkedQueue<Integer> queue = new ConcurrentLinkedQueue<Integer>();
        for (int i=1;i<21;i++){
            queue.add(i);
        }
        System.out.println(" Elements in queue : " + queue);
        for (int i = 1; i < 11; i++) {
            int j = i *5;
            list.add(j);
        }
        //will give the elements int the queue which are present in list
        queue.retainAll(list);
        System.out.println(" Multiple of 5 : " + queue);
    }
}

Output:

Elements in queue : [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
 Multiple of 5 : [5, 10, 15, 20]

Example 2

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ConcurrentLinkedQueue;
public class ConcurrentLinkedQueueRetainAllExample2 {
    static int i=1;
    public static void main(String[] args) {
        List<String> list = new ArrayList<String>();
        ConcurrentLinkedQueue<String> queue = new ConcurrentLinkedQueue<String>();
        queue.add("Reema");
        queue.add("Ranjeeta");
        queue.add("Rani");
        queue.add("Sukla");
        queue.add("Raj");
        System.out.println("Students in the class : ");
        for (String str : queue){
            System.out.println(i++ +"."+str);
        }
        list.add("Raj");
        list.add("Rani");
        list.add("Ranjeeta");
        queue.retainAll(list);
        System.out.println("Students failed : ");
        i=1;
        for (String str : queue){
            System.out.println(i++ +"."+str);
        }
    }
}

Output:

1.Reema
2.Ranjeeta
3.Rani
4.Sukla
5.Raj
Students failed : 
1.Ranjeeta
2.Rani
3.Raj

Example 3

import java.util.TreeSet;
import java.util.concurrent.ConcurrentLinkedQueue;
public class ConcurrentLinkedQueueRetainAllExample3 {
    public static void main(String[] args) {
        TreeSet<Integer> list = new TreeSet<Integer>();
        ConcurrentLinkedQueue<Integer> queue = new ConcurrentLinkedQueue<Integer>();
        for (int i=1;i<21;i++){
            queue.add(i);
        }
        list.add(101);
        list.add(null);
        queue.retainAll(list);
        System.out.println("Queue = "+queue);
    }
}

Output:

Exception in thread "main" java.lang.NullPointerException
	at java.util.TreeMap.put(TreeMap.java:563)
	at java.util.TreeSet.add(TreeSet.java:255)
	at com.javaTpoint.ConcurrentLinkedQueueRetainAllExample3.main(ConcurrentLinkedQueueRetainAllExample3.java:13)

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