Java ArrayBlockingQueue retainAll() Method

The retainAll() method of Java ArrayBlockingQueue class retains only the elements of the ArrayBlockingQueue that are contained in the specified collection and removes rest of the elements.

Syntax:

Parameters:

Here, the parameter c is the collection containing elements to be retained in the ArrayBlockingQueue collection.

Specified By:

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

Return Value:

The retainAll () method returns a Boolean value 'true' if the collection has changed as a result of the call, else it returns 'false'.

Throws:

It throws NullPointerException, if the specified collection does not support null elements or it contains one or more null elements.

Example 1

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ArrayBlockingQueue;

public class ArrayBlockingQueueRetainAllExample1 {
    public static void main(String[] args) throws InterruptedException {
        List<Integer> list = new ArrayList<Integer>();
        int capacity = 100;
        ArrayBlockingQueue<Integer> queue = new ArrayBlockingQueue<Integer>(capacity);
        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 in 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.Queue;
import java.util.concurrent.ArrayBlockingQueue;

public class ArrayBlockingQueueRetainAllExample2 {
    public static void main(String[] args) {
        List<String> list = new ArrayList<String>();
        int capacity = 100;
        ArrayBlockingQueue<String> queue = new ArrayBlockingQueue<String>(capacity);
            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(str);
        }
        list.add("Raj");
        list.add("Rani");
        list.add("Ranjeeta");
        queue.retainAll(list);
        System.out.println("Students failed : ");
        for (String str : queue){
            System.out.println(str);
        }
    }
}

Output:

Students in the class : 
Reema
Ranjeeta
Rani
Sukla
Raj
Students failed : 
Ranjeeta
Rani
Raj

Example 3

import java.util.TreeSet;
import java.util.concurrent.ArrayBlockingQueue;

public class ArrayBlockingQueueRetainAllExample3 {
    public static void main(String[] args) {
        TreeSet<Integer> list = new TreeSet<Integer>();
        int capacity = 100;
        ArrayBlockingQueue<Integer> queue = new ArrayBlockingQueue<Integer>(capacity);
        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.ArrayBlockingQueueRetainAllExample3.main(ArrayBlockingQueueRetainAllExample3.java:15)

As TreeSet does not permit null elements, so it will give NullPointerException as shown above.

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