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CopyOnWriteArrayList addAllAbsent() method in Java with Examples

Last Updated : 11 Jul, 2025

The

addAllAbsent(E e)

method of

CopyOnWriteArrayList

appends all of the elements in the specified collection that are not already contained in this list, to the end of this list, in the order that they are returned by the specified collection's iterator.

Syntax:

public int addAllAbsent(Collection<E> collection)

Parameters:

The function accepts a single mandatory parameter

collection

which specifies the collection to be appended to the list if it is not present.

Return Value:

The function returns

an integer value

which is the number if elements added in the List.

Exception:

This method throws

NullPointerException

if the specified collection is null. Below programs illustrate the addAllAbsent() function:

Program 1: Java


 // Java Program to illustrate the CopyOnWriteArrayList
// addAllAbsent() method in Java

import java.util.concurrent.CopyOnWriteArrayList;
import java.util.*;

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

        // create object of CopyOnWriteArrayList
        CopyOnWriteArrayList<Integer> ArrLis
            = new CopyOnWriteArrayList<Integer>();

        // Add elements
        ArrLis.add(2);
        ArrLis.add(3);
        ArrLis.add(4);
        ArrLis.add(7);

        // print CopyOnWriteArrayList
        System.out.println("CopyOnWriteArrayList: "
                           + ArrLis);

        // creating an Empty Integer ArrayList
        ArrayList<Integer> arr = new ArrayList<Integer>(4);

        // using add() to initialize values
        // [1, 2, 3, 4]
        arr.add(1);
        arr.add(2);
        arr.add(3);
        arr.add(4);

        // list initially
        System.out.println("The collection to be appended: "
                           + arr);

        // Append the list arr in the list ArrLis
        // using addAllAbsent() method
        System.out.println("\nNumber of elements appended"
                           + " using addAllAbsent() method: "
                           + ArrLis.addAllAbsent(arr));

        // print CopyOnWriteArrayList
        System.out.println("Modified CopyOnWriteArrayList: "
                           + ArrLis);
    }
}

Output:

CopyOnWriteArrayList: [2, 3, 4, 7]
The collection to be appended: [1, 2, 3, 4]

Number of elements appended using addAllAbsent() method: 1
Modified CopyOnWriteArrayList: [2, 3, 4, 7, 1]

Program 2:

To demonstrate NullPointerException

Java


 // Java Program to illustrate the CopyOnWriteArrayList
// addAllAbsent() method in Java

import java.util.concurrent.CopyOnWriteArrayList;
import java.util.*;

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

        // create object of CopyOnWriteArrayList
        CopyOnWriteArrayList<Integer> ArrLis
            = new CopyOnWriteArrayList<Integer>();

        // Add elements
        ArrLis.add(2);
        ArrLis.add(3);
        ArrLis.add(4);
        ArrLis.add(7);

        // print CopyOnWriteArrayList
        System.out.println("CopyOnWriteArrayList: "
                           + ArrLis);

        // creating a null Integer ArrayList
        ArrayList<Integer> arr = null;

        // list initially
        System.out.println("The collection to be appended: "
                           + arr);

        try {
            // Append the list arr in the list ArrLis
            // using addAllAbsent() method
            System.out.println("\nTrying to append null collection\n");
            ArrLis.addAllAbsent(arr);
        }
        catch (Exception e) {
            System.out.println(e);
        }
    }
}

Output:

CopyOnWriteArrayList: [2, 3, 4, 7]
The collection to be appended: null

Trying to append null collection

java.lang.NullPointerException

Reference: https://docs.oracle.com/javase/9/docs/api/java/util/concurrent/CopyOnWriteArrayList.html#addAllAbsent-java.util.Collection-

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