ArrayList toArray() method in Java with Examples

The toArray() method of ArrayList is used to return an array containing all the elements in ArrayList 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 ArrayList.toArray() method:

Program 1:

// Java Program to illustrate the
// ArrayList toArray() method in Java

import java.util.*;

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

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

        // Add elements
        ArrLis.add(32);
        ArrLis.add(67);
        ArrLis.add(98);
        ArrLis.add(100);

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

        // Get the array of the elements
        // of the ArrayList
        // using toArray() method
        Object[] arr = ArrLis.toArray();

        System.out.println("Elements of ArrayList"
                           + " as Array: "
                           + Arrays.toString(arr));
    }
}

Output:

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

Program 2:

// Java Program to illustrate the
// ArrayList toArray(T[]) method in Java

import java.util.*;

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

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

        // Add elements
        ArrLis.add(32);
        ArrLis.add(67);
        ArrLis.add(98);
        ArrLis.add(100);

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

        // Get the array of the elements
        // of the ArrayList
        // using toArray(T[]) method
        Integer arr[] = new Integer[ArrLis.size()];
        arr = ArrLis.toArray(arr);

        System.out.println("Elements of ArrayList"
                           + " as Array: "
                           + Arrays.toString(arr));
    }
}

Output:

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

Reference:

• https://docs.oracle.com/javase/9/docs/api/java/util/ArrayList.html#toArray–
• https://docs.oracle.com/javase/9/docs/api/java/util/ArrayList.html#toArray-T:A-