The List interface provides a way to store the ordered collection. It is a child interface of Collection. It is an ordered collection of objects in which duplicate values can be stored. Since List preserves the insertion order, it allows positional access and insertion of elements. Now here we are given a List be it any LinkedList or ArrayList of strings, our motive is to convert this list to an array of strings in java using different methods.
Methods:
- Using get() method
- Using toArray() method
- Using Stream introduced in Java 8
Method 1: Using get() method
We can use the below list method to get all elements one by one and insert them into an array.
Return Type: The element at the specified index in the list.
Syntax:
public E get(int index)
Example:
Java
// Java program to Convert a List to an Array// Using get() method in a loop// Importing required classesimport java.io.*;import java.util.LinkedList;import java.util.List;// Main classclass GFG { // Main driver method public static void main(String[] args) { // Creating a LinkedList of string type by // declaring object of List List<String> list = new LinkedList<String>(); // Adding custom element to LinkedList // using add() method list.add("Geeks"); list.add("for"); list.add("Geeks"); list.add("Practice"); // Storing it inside array of strings String[] arr = new String[list.size()]; // Converting ArrayList to Array // using get() method for (int i = 0; i < list.size(); i++) arr[i] = list.get(i); // Printing elements of array on console for (String x : arr) System.out.print(x + " "); }} |
Geeks for Geeks Practice
The time complexity and space complexity of this Java code is O(n), where n is the size of the list.
Method 2: Using toArray() method
Example:
Java
// Java Program to Convert a List to an array// using toArray() Within a loop// Importing utility classesimport java.util.*;// Main classpublic class GFG { // Main driver method public static void main(String[] args) { // Creating an empty LinkedList of string type // by declaring object of List List<String> list = new LinkedList<String>(); // Adding elements to above LinkedList // using add() method list.add("Geeks"); list.add("for"); list.add("Geeks"); list.add("Practice"); // Converting List to array // using toArray() method String[] arr = list.toArray(new String[0]); // Printing elements of array // using for-each loop for (String x : arr) System.out.print(x + " "); }} |
Geeks for Geeks Practice
The time complexity and space complexity of this Java code is O(n), where n is the size of the list.
Method 3: Using Stream introduced in Java8
Example:
Java
// Java Program to Demonstrate conversion of List to Array// Using stream// Importing utility classesimport java.util.*;// Main classclass GFG { // Main driver method public static void main(String[] args) { // Creating an empty LinkedList of string type List<String> list = new LinkedList<String>(); // Adding elements to above LinkedList // using add() method list.add("Geeks"); list.add("for"); list.add("Geeks"); list.add("Practice"); // Storing size of List int n = list.size(); // Converting List to array via scope resolution // operator using streams String[] arr = list.stream().toArray(String[] ::new); // Printing elements of array // using enhanced for loop for (String x : arr) System.out.print(x + " "); }} |
Geeks for Geeks Practice
Tip: We can convert the array back to the list via asList() method.
The time complexity and space complexity of this Java code is O(n), where n is the size of the list.
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