AbstractSequentialList toArray(T[]) method in Java with Example

The toArray(arr[]) method of AbstractSequentialList class in Java is used to form an array of the same elements as that of the AbstractSequentialList. It returns an array containing all of the elements in this AbstractSequentialList in the correct order; the run-time type of the returned array is that of the specified array. If the AbstractSequentialList fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the run time type of the specified array and the size of this AbstractSequentialList. If the AbstractSequentialList fits in the specified array with room to spare (i.e., the array has more elements than the AbstractSequentialList), the element in the array immediately following the end of the AbstractSequentialList is set to null. (This is useful in determining the length of the AbstractSequentialList only if the caller knows that the AbstractSequentialList does not contain any null elements.) Syntax:

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

Parameters: The method accepts one parameter arr[] which is the array into which the elements of the AbstractSequentialList 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 method returns an array containing the elements similar to the AbstractSequentialList. Exception: The method might throw two types of exception:

• ArrayStoreException: When the mentioned array is of the different type and is not able to compare with the elements mentioned in the AbstractSequentialList.
• NullPointerException: If the array is Null, then this exception is thrown.

Below program illustrates the working of the AbstractSequentialList.toArray(arr[]) method. Program 1: When array is of the size of AbstractSequentialList 

Java

// Java code to illustrate toArray(arr[])

import java.util.*;

public class AbstractSequentialListDemo {
    public static void main(String args[])
    {
        // Creating an empty AbstractSequentialList
        AbstractSequentialList<String>
            abs_col = new LinkedList<String>();

        // Use add() method to add
        // elements into the AbstractSequentialList
        abs_col.add("Welcome");
        abs_col.add("To");
        abs_col.add("Geeks");
        abs_col.add("For");
        abs_col.add("Geeks");

        // Displaying the AbstractSequentialList
        System.out.println("The AbstractSequentialList: "
                           + abs_col);

        // Creating the array and using toArray()
        String[] arr = new String[5];
        arr = abs_col.toArray(arr);

        // Displaying arr
        System.out.println("The arr[] is:");
        for (int j = 0; j < arr.length; j++)
            System.out.println(arr[j]);
    }
}

Output:

The AbstractSequentialList: [Welcome, To, Geeks, For, Geeks]
The arr[] is:
Welcome
To
Geeks
For
Geeks

Program 2: When array is less than the size of AbstractSequentialList 

Java

// Java code to illustrate toArray(arr[])

import java.util.*;

public class AbstractSequentialListDemo {
    public static void main(String args[])
    {
        // Creating an empty AbstractSequentialList
        AbstractSequentialList<String>
            abs_col = new LinkedList<String>();

        // Use add() method to add
        // elements into the AbstractSequentialList
        abs_col.add("Welcome");
        abs_col.add("To");
        abs_col.add("Geeks");
        abs_col.add("For");
        abs_col.add("Geeks");

        // Displaying the AbstractSequentialList
        System.out.println("The AbstractSequentialList: "
                           + abs_col);

        // Creating the array and using toArray()
        String[] arr = new String[1];
        arr = abs_col.toArray(arr);

        // Displaying arr
        System.out.println("The arr[] is:");
        for (int j = 0; j < arr.length; j++)
            System.out.println(arr[j]);
    }
}

Output:

The AbstractSequentialList: [Welcome, To, Geeks, For, Geeks]
The arr[] is:
Welcome
To
Geeks
For
Geeks

Program 3: When array is more than the size of AbstractSequentialList 

Java

// Java code to illustrate toArray(arr[])

import java.util.*;

public class AbstractSequentialListDemo {
    public static void main(String args[])
    {
        // Creating an empty AbstractSequentialList
        AbstractSequentialList<String>
            abs_col = new LinkedList<String>();

        // Use add() method to add
        // elements into the AbstractSequentialList
        abs_col.add("Welcome");
        abs_col.add("To");
        abs_col.add("Geeks");
        abs_col.add("For");
        abs_col.add("Geeks");

        // Displaying the AbstractSequentialList
        System.out.println("The AbstractSequentialList: "
                           + abs_col);

        // Creating the array and using toArray()
        String[] arr = new String[10];
        arr = abs_col.toArray(arr);

        // Displaying arr
        System.out.println("The arr[] is:");
        for (int j = 0; j < arr.length; j++)
            System.out.println(arr[j]);
    }
}

Output:

The AbstractSequentialList: [Welcome, To, Geeks, For, Geeks]
The arr[] is:
Welcome
To
Geeks
For
Geeks
null
null
null
null
null

Program 4: To demonstrate NullPointerException 

Java

// Java code to illustrate toArray(arr[])

import java.util.*;

public class AbstractSequentialListDemo {
    public static void main(String args[])
    {
        // Creating an empty AbstractSequentialList
        AbstractSequentialList<String>
            abs_col = new LinkedList<String>();

        // Use add() method to add
        // elements into the AbstractSequentialList
        abs_col.add("Welcome");
        abs_col.add("To");
        abs_col.add("Geeks");
        abs_col.add("For");
        abs_col.add("Geeks");

        // Displaying the AbstractSequentialList
        System.out.println("The AbstractSequentialList: "
                           + abs_col);

        try {
            // Creating the array
            String[] arr = null;
            // using toArray()
            // Since arr is null
            // Hence exception will be thrown
            arr = abs_col.toArray(arr);

            // Displaying arr
            System.out.println("The arr[] is:");
            for (int j = 0; j < arr.length; j++)
                System.out.println(arr[j]);
        }
        catch (Exception e) {
            System.out.println("Exception: " + e);
        }
    }
}

Output:

The AbstractSequentialList: [Welcome, To, Geeks, For, Geeks]
Exception: java.lang.NullPointerException