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

CopyOnWriteArraySet removeAll() method in Java with Examples

Last Updated : 11 Jul, 2025

The

removeAll()

method of

CopyonWriteArraySet

method removes all the elements of this CopyOnWriteArraySet that are present in the specified collection. That means elements which are common in both the collections are removed from this CopyOnWriteArraySet.

Syntax:

public boolean removeAll(Collection<E> c)

Parameters:

This method accepts a parameter

which is the collection containing elements to be removed from 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 following Exceptions:

ClassCastException: if the class of an element of this set is incompatible with the specified collection
NullPointerException: if this set contains a null element and the specified collection does not permit null elements, or if the specified collection is null.

Below program illustrates the removeAll() function of CopyOnWriteArrayList class:

Program 1: Java


 // Java Program to illustrate the CopyOnWriteArraySet
// removeall() 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(10);
        Arrlist.add(30);
        Arrlist.add(40);

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

        // removing the common elements from
        // the CopyOnWriteArraySet using removeAll()
        System.out.println("Elements removed "
                           + "from CopyOnWriteArraySet: "
                           + ArrSet.removeAll(Arrlist));

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

Output:

CopyOnWriteArraySet: [10, 20, 30, 50]
ArrayList: [10, 30, 40]
Elements removed from CopyOnWriteArraySet: true
Updated CopyOnWriteArraySet: [20, 50]

Program 2:

To show NullpointerException

Java


 // Java Program to illustrate the CopyOnWriteArraySet
// removeall() 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);

        try {

            // removing the null from
            // the CopyOnWriteArraySet using removeAll()
            // This will throw NullPointerException

            System.out.println("Elements removed "
                               + "from CopyOnWriteArraySet: "
                               + ArrSet.removeAll(null));
        }
        catch (Exception e) {
            System.out.println(e);
        }
    }
}

Output:

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

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