CopyOnWriteArrayList toArray() method in Java

Difficulty Level : Medium
Last Updated : 18 Dec, 2018

The toArray() method of CopyOnWriteArrayList is used to return an array containing all the elements in CopyOnWriteArrayList in the correct order.

Syntax:

public Object[] toArray()
           or
public <T> T[] toArray(T[] a)

Parameters: This method either accepts no parameters or it takes an array T[] a as parameter which is the array into which the elements of the list are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.

Return Value: The function returns an array containing all the elements in this list.

Exception: The first overload of this method throws no exceptions. However, the second overload throws following exceptions:

ArrayStoreException: if the runtime type of the specified array is not a supertype of the runtime type of every element in this list.
NullPointerException if the specified array is null

Below programs illustrate the CopyOnWriteArrayList.toArray() method:

Program 1:

// Java Program to illustrate the
// CopyOnWriteArrayList toArray() 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(32);
        ArrLis.add(67);
        ArrLis.add(98);
        ArrLis.add(100);
  
        // print CopyOnWriteArrayList
        System.out.println("CopyOnWriteArrayList: "
                           + ArrLis);
  
        // Get the array of the elements
        // of the CopyOnWriteArrayList
        // using toArray() method
        Object[] arr = ArrLis.toArray();
  
        System.out.println("Elements of CopyOnWriteArrayList"
                           + " as Array: "
                           + Arrays.toString(arr));
    }
}

Output:

CopyOnWriteArrayList: [32, 67, 98, 100]
Elements of CopyOnWriteArrayList as Array: [32, 67, 98, 100]

Program 2:

// Java Program to illustrate the
// CopyOnWriteArrayList toArray(T[]) 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(32);
        ArrLis.add(67);
        ArrLis.add(98);
        ArrLis.add(100);
  
        // print CopyOnWriteArrayList
        System.out.println("CopyOnWriteArrayList: "
                           + ArrLis);
  
        // Get the array of the elements
        // of the CopyOnWriteArrayList
        // using toArray(T[]) method
        Integer arr[] = new Integer[ArrLis.size()];
        arr = ArrLis.toArray(arr);
  
        System.out.println("Elements of CopyOnWriteArrayList"
                           + " as Array: "
                           + Arrays.toString(arr));
    }
}

Output:

CopyOnWriteArrayList: [32, 67, 98, 100]
Elements of CopyOnWriteArrayList as Array: [32, 67, 98, 100]

Reference: CopyOnWriteArrayList.toArray() doc, CopyOnWriteArrayList.toArray(T[]) doc

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