Java Program to Convert an Array into a List

In Java, arrays and lists are two commonly used data structures. While arrays have a fixed size and are simple to use, lists are dynamic and provide more flexibility. There are times when you may need to convert an array into a list, for instance, when you want to perform operations like adding or removing elements dynamically. In this article, we’ll explore how to convert an array into a list in Java.

Example 1: Using Arrays.asList() Method

One of the most easy and effective ways to convert an array into a list in Java is by using the Arrays.asList() method. This method provides a fixed-size list backed by the specified array.

import java.util.Arrays; 
import java.util.List;

public class ArrayToList {
  
    public static void main(String[] args) {
      
        // Array declaration
        String[] arr = {"geeks", "for", "geeks", "for", "dev"};
        
        // Converting using array to list using Arrays.asList()
        List<String> lis = Arrays.asList(arr);
        
        System.out.println("List: " + lis);
    }
}

List: [geeks, for, geeks, for, dev]

Explanation: The Arrays.asList() method converts the given array into a list. The returned list is backed by the original array, which mean that changes to the list will affect the array.

Example 2: Using ArrayList Constructor

If you want to add or remove the elements, you can use the ArrayList constructor to convert an array into a list. The ArrayList constructor can accept a collection, and we can pass a list created from the array.

import java.util.*;

public class ArrayToList{
  
    public static void main(String[] args) {
      
        // Taking an array
        Integer[] arr = {1, 2, 3, 4, 5, 6, 7, 8};
        
        // Converting array to ArrayList
        List<Integer> lis = new ArrayList<>(Arrays.asList(arr));
        
        System.out.println("List: " + lis);
        
        // Adding a new element to the ArrayList
        lis.add(9);
        
        // Printing the updated list
        System.out.println("Updated List: " + lis);
    }
}

List: [1, 2, 3, 4, 5, 6, 7, 8]
Updated List: [1, 2, 3, 4, 5, 6, 7, 8, 9]

Explanation:

• Here, we first use Arrays.asList() to convert the array into a list. Then, we pass that list to the ArrayList constructor to create an ArrayList, which allows us to modify the list by adding new elements.
• This method provides the flexibility of adding or removing elements from the list, which is not possible with Arrays.asList() alone.

Example 3: Using Stream API (Java 8 and above)

If you are using the Java 8 or later, you can also use the Stream API to convert an array into a list in a functional style.

import java.util.*;
import java.util.stream.*;

public class ArrayToList {
  
    public static void main(String[] args) {
        // array declaration
        Double[] arr = {1.1, 2.2, 3.3, 4.4, 5.5};
        
        // Converting array to list using Stream API
        List<Double> lis = Arrays.stream(arr).collect(Collectors.toList());
      
        System.out.println("List: " + lis);
    }
}

List: [1.1, 2.2, 3.3, 4.4, 5.5]

Explanation:

• The Arrays.stream() method creates a stream from the array, and Collectors.toList() collects the elements of the stream into a list.
• This is a clean and efficient way to convert an array to a list, especially when you want to apply additional operations on the stream before collecting the results.

Example 4: Using Collections.addAll() Method

If you want to add elements of an array to an existing list, the Collections.addAll() method is a great choice. It accepts the list and the array as parameters.

import java.util.*;

public class ArrayToList {
  
    public static void main(String[] args) {
      
        // Taking an array
        String[] arr = {"Geeks", "forGeeks", "A computer Portal" };
        
        // Creating an ArrayList and adding array elements to it
        List<String> lis = new ArrayList<>();
        Collections.addAll(lis, arr);
        
        // Printing the list
        System.out.println("List: " + lis);
    }
}

List: [Geeks, forGeeks, A computer Portal]

Example 5: Using List.of() Method (Java 9+)

From Java 9 onwards, you can use the List.of() method to create immutable lists directly from the array.

import java.util.*;

public class ArrayToList{
  
    public static void main(String[] args) {
      
        // taking an array
        String[] arr = {"geeks", "for", "geeks"};
        
        // Converting array to immutable list
        List<String> list = List.of(arr);
        
        System.out.println("List: " + list);
    }
}

List: [geeks, for, geeks]