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Showing content from https://www.geeksforgeeks.org/java/copyonwritearrayset-addall-method-in-java-with-examples/ below:

CopyOnWriteArraySet addAll() method in Java with Examples

Last Updated : 11 Jul, 2025

The

addAll()

method of

CopyonWriteArraySet

method adds all the element of the specified collection to this CopyOnWriteArraySet which are not present in it. This methods results the union of the two collections.

Syntax:

public boolean addAll(Collection<E> c)

Parameters:

This method accepts a parameter

which is the collection containing elements to be added to this set.

Return Value:

This method returns a

boolean value

such as true, if the CopyOnWriteArraySet is changed. Else this method returns false.

Exceptions:

This method throws

NullPointerException

if the specified collection is null. Below program illustrates the addAll() function of CopyOnWriteArrayList class:

Program 1:

In the below program, the specified collection elements are added to the CopyOnWriteArraySet. Since 50 is common in both the collections, it is added single time.

Java


 // Java Program to illustrate the
// CopyOnWriteArraySet addall() method in Java

import java.util.concurrent.CopyOnWriteArraySet;
import java.util.*;

public class GFG {
    public static void main(String[] args)
    {

        // create object of CopyOnWriteArraySet
        CopyOnWriteArraySet<Integer> ArrSet
            = new CopyOnWriteArraySet<Integer>();

        // Add elements
        ArrSet.add(10);
        ArrSet.add(20);
        ArrSet.add(30);
        ArrSet.add(50);

        // print CopyOnWriteArraySet
        System.out.println("CopyOnWriteArraySet: "
                           + ArrSet);

        // create object of ArrayList
        ArrayList<Integer> Arrlist
            = new ArrayList<Integer>();

        // Add elements
        Arrlist.add(50);
        Arrlist.add(60);
        Arrlist.add(70);
        Arrlist.add(80);

        // print ArrayList
        System.out.println("ArrayList:  "
                           + Arrlist);

        // adding all elements of Arraylist
        // in the CopyOnWriteArraySet
        ArrSet.addAll(Arrlist);

        // print updated CopyOnWriteArraySet
        System.out.println("Updated CopyOnWriteArraySet: "
                           + ArrSet);
    }
}

Output:

CopyOnWriteArraySet: [10, 20, 30, 50]
ArrayList:  [50, 60, 70, 80]
Updated CopyOnWriteArraySet: [10, 20, 30, 50, 60, 70, 80]

Program 2:

To show NullpointerException

Java


 // Java Program to illustrate the
// CopyOnWriteArraySet addall() method in Java

import java.util.concurrent.CopyOnWriteArraySet;
import java.util.*;

public class GFG {
    public static void main(String[] args)
    {

        // create object of CopyOnWriteArraySet
        CopyOnWriteArraySet<Integer> ArrSet
            = new CopyOnWriteArraySet<Integer>();

        // Add elements
        ArrSet.add(10);
        ArrSet.add(20);
        ArrSet.add(30);
        ArrSet.add(50);

        // print CopyOnWriteArraySet
        System.out.println("CopyOnWriteArraySet: "
                           + ArrSet);

        // create object of ArrayList
        ArrayList<Integer> Arrlist
            = new ArrayList<Integer>();

        try {

            // adding null to the CopyOnWriteArraySet
            // This will throw NullPointerException
            ArrSet.addAll(null);
        }
        catch (Exception e) {
            System.out.println(e);
        }
    }
}

Output:

CopyOnWriteArraySet: [10, 20, 30, 50]
java.lang.NullPointerException

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