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

// 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));
    }
}

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

// 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);
    }
}

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