CopyOnWriteArrayList add() method in Java

The add(E e) method of CopyOnWriteArrayList inserts the element passed in the parameter to the end of the List or at a specified index in the list. The function returns true on addition of new element to the list.

Syntax:

public boolean add(E e)
          or
public void add(int index, E element)

Parameters: The function accepts two types of parameters which are described below:

• index: specifies the index at which the element is to be added. The parameter is not mandatory. If this parameter is not passed, then the addition is done at the end of the list.
• element: specifies the element to be added in the list

Return Value: The function returns true on addition in the list.

Below programs illustrate the above function:

Program 1:

// Java Program to illustrate the CopyOnWriteArrayList
// add(element) 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);

        System.out.println("On adding 45 it returns "
                                     + ArrLis.add(45));
    }
}

Output:

CopyOnWriteArrayList: [2, 3, 4, 7]
On adding 45 it returns true

Program 2:

// Java Program to illustrate the CopyOnWriteArrayList
// add(index, element) 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 at 0th index
        ArrLis.add(0, 2);
        System.out.println("CopyOnWriteArrayList: " + ArrLis);

        // Add elements at 0th index
        ArrLis.add(0, 3);
        System.out.println("CopyOnWriteArrayList: " + ArrLis);

        // Add elements at 1st index
        ArrLis.add(1, 4);
        System.out.println("CopyOnWriteArrayList: " + ArrLis);

        // Add elements at 2nd index
        ArrLis.add(2, 7);
        System.out.println("CopyOnWriteArrayList: " + ArrLis);
    }
}

Output:

CopyOnWriteArrayList: [2]
CopyOnWriteArrayList: [3, 2]
CopyOnWriteArrayList: [3, 4, 2]
CopyOnWriteArrayList: [3, 4, 7, 2]

Reference: https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/CopyOnWriteArrayList.html#add-E-