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LinkedList toArray() method in Java with Example

  • Difficulty Level : Medium
  • Last Updated : 24 Dec, 2018

1 : Using toArray()

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The Java.util.LinkedList.toArray() method returns an array containing all the elements in the list in proper sequence i.e. from first to last. The returned array will be safe as a new array is created (hence new memory is allocated). Thus the caller is free to modify the array. It acts as a bridge between array-based and collection-based APIs.

Syntax



public Object[] toArray()

Parameters:It does not take in any parameter.

Return Value:It returns an array containing all the elements in the list.

Below examples illustrates the LinkedList.toArray() method:

Example 1:




// Java Program Demonstrate toArray()
// method of LinkedList
  
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
        throws IllegalStateException
    {
  
        // create object of LinkedList
        LinkedList<Integer> list
            = new LinkedList<Integer>();
  
        // Add numbers to end of LinkedList
        list.add(7855642);
        list.add(35658786);
        list.add(5278367);
        list.add(74381793);
  
        System.out.println("LinkedList: "
                           + list);
  
        Object[] a = list.toArray();
        System.out.println("Returned Array: "
                           + Arrays.toString(a));
    }
}
Output:
LinkedList: [7855642, 35658786, 5278367, 74381793]
Returned Array: [7855642, 35658786, 5278367, 74381793]

2 : Using toArray(T[])

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

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

Parameters: The method accepts one parameter arr[] which is the array into which the elements of the LinkedList 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 LinkedList.

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 LinkedList.
  • NullPointerException: If the array is Null, then this exception is thrown.

Below program illustrates the working of the LinkedList.toArray(arr[]) method.

Program 1: When array is of the size of LinkedList




// Java code to illustrate toArray(arr[])
  
import java.util.*;
  
public class LinkedListDemo {
    public static void main(String args[])
    {
        // Creating an empty LinkedList
        LinkedList<String> list
            = new LinkedList<String>();
  
        // Use add() method to add
        // elements into the LinkedList
        list.add("Welcome");
        list.add("To");
        list.add("Geeks");
        list.add("For");
        list.add("Geeks");
  
        // Displaying the LinkedList
        System.out.println("The LinkedList: "
                           + list);
  
        // Creating the array and using toArray()
        String[] arr = new String[5];
        arr = list.toArray(arr);
  
        // Displaying arr
        System.out.println("Returned Array: "
                           + Arrays.toString(arr));
    }
}
Output:
The LinkedList: [Welcome, To, Geeks, For, Geeks]
Returned Array: [Welcome, To, Geeks, For, Geeks]



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