Convert array to list in Java

In this post, you will learn how to convert an array to a list using the Java programming language.

Arrays and lists are the most commonly used data structures in Java. An array is a container that can hold a fixed number of items, and these items should be of the same type. Once an array is created, we cannot change its size. In Java, an array can hold primitives or objects.

A list is a sequence of indexed and ordered values. Java List is an interface that extends the Collection interface. It contains a list of any type of data object with a comma separated and enclosed within a square bracket. Java List provides control over the position where you can insert an element. In the development process, we may come across a situation where we need to convert an array to a list.

Converting array to list using native method

In the given Java program, we have used the naïve approach to convert an array to a list. First, we create an empty list and iterate through the items in the array. In each iteration, we add the element to the list.

// Java Program to convert
// array to list
  
import java.util.*;
import java.util.stream.*;
  
class ArrayToList {
  
    // Generic function to convert an Array to List
    public static <T> List<T> convertArrayToList(T array[])
    {
        // Create an empty List
        List<T> list = new ArrayList<>();
  
        // Iterate through the array
        for (T t : array) {
            // Add each element into the list
            list.add(t);
        }
        // Return the converted List
        return list;
    }
  
    public static void main(String args[])
    {
        // Create an Array
        String array[]
            = { "apple","orange","guava","orange","kiwi" };
  
        // Print the Array
        System.out.println("Array: "
                           + Arrays.toString(array));
  
        // Convert the Array to List
        List<String> list = convertArrayToList(array);
  
        // Print the List
        System.out.println("List: " + list);
    }
}

Array: [apple, orange, guava, orange, kiwi]
List: [apple, orange, guava, orange, kiwi]

Converting array to list using Arrays.asList() method

The java.util.Arrays.asList returns a fixed-size list that is​ backed by the specified array. This method acts as a bridge between array-based and collection-based APIs. Here, we use the Arrays.asList() method of Java to convert an array to a list.

import java.util.*;   
public class ConvertArrayToList
{   
    public static void main(String args[])   
    {   
     //creating an array to be converted  
     String arr[] = {"Apple","Orange","Mango","Guava","Kiwi" };   
     //print array before conversion  
     System.out.println("Array: "+ Arrays.toString(arr)); 
    
     //converts Array into List using generic method   
     List<String> list = ArrayToListConversion(arr);   
    
     //prints the List  
     System.out.println("List: " + list);   
    }   
    
    // creating a generic function 
    // to converts the Array into List  
    public static <T> List<T> ArrayToListConversion(T arr[])   
    {   
     // invoking the asList() method 
     // passing the array to be converted  
     List<T> list = Arrays.asList(arr);   
     //returns the list  
     return list;   
    }   
}  

Converting array to list using Collections.addAll() method

A collection represents a group of objects, known as its elements. Collections is a utility class that resides in the java.util package. It consists entirely of static methods which are used to operate on collections. In the given Java program, we have used the addAll() method of collections to convert an array to a list.

import java.util.*;   
public class ConvertArrayToList  
{   
    public static void main(String args[])   
    {   
        // Initializing an array  
        String arr[] = {"Pineapple","Jackfruit","Orange","Mango","Pear"};   
        
        // print the Array   
        System.out.println("Array: "+ Arrays.toString(arr));  
        
        // calling method  
        List<String> list = ArrayToListConversion(arr);   
        // print the List   
        System.out.println("List: " + list);   
    }       
    // Creating a generic function 
    // to convert the array into list  
    public static <T> List<T> ArrayToListConversion(T arr[])   
    {   
        // Creating the constructor of the List class  
        List<T> list = new ArrayList<>();   
        //the addAll() method adds Array to the List  
        Collections.addAll(list, arr);   
        //returns the list  
        return list;   
    }   
}  

Array: [Pineapple, Jackfruit, Orange, Mango, Pear]
List: [Pineapple, Jackfruit, Orange, Mango, Pear]

Converting array to list using Java 8 Stream API

Java 8 introduces the Stream API. The Stream API provides many methods which can be pipelined to produce the desired result. We can use the Collectors.toList() method of the Steam API to convert an array to a list. The method returns a Collector that collects the input elements into a newly created list in an encounter method. The Collectors.toList() method returns a Collector that collects the input elements into a newly created List in an encounter method.

// Java Program to convert
// Array to List in Java 8
  
import java.util.*;
import java.util.stream.*;
  
class ConvertArrayToList {
  
    // Generic function to convert array to list
    public static  List convertArrayToList(T array[])
    {
        // create a list from the Array
        return Arrays.stream(array).collect(
            Collectors.toList());
    }
  
    public static void main(String args[])
    {
        // Initialize an Array
        String arr[]
            = { "Peas","Onion","Potato","Tomato","Beans" };
  
        // Print the Array
        System.out.println("Array: "
                           + Arrays.toString(arr));
  
        // Convert the Array to List
        List list = convertArrayToList(arr);
  
        // Print the List
        System.out.println("List: " + list);
    }
}

Array: [Peas, Onion, Potato, Tomato, Beans]
List: [Peas, Onion, Potato, Tomato, Beans]

Converting array to list using the Guava Lists.newArrayList() method

Guava is a set of core Java libraries from Google that includes new collection types, immutable collections, a graph library, and much more. The Lists.newArrayList() is a method of the Lists class that belongs to the com.google.common.collect package. In the given Java program, we create an empty list and add the array into the list by passing it as the parameter to the Lists.newArrayList() method.

// Java Program to convert
// array to list

import static com.google.common.collect.Lists.*;   
import java.util.*;   
public class ArrayToList
{   
    public static void main(String args[])   
    {   
        //Initializing array 
        String arr[] = { "One","Two","Three","Four","Five"};  
        
        // Array before conversion  
        System.out.println("Array: "+ Arrays.toString(arr));  
        
        //convert the Array to List   
        List list = ArrayToListConversion(arr);   

        System.out.println("List: " + list);   
    }  
        
    // Creating a generic function 
    // to converts the Array into List  
    public static  List ArrayToListConversion(T arr[])   
    {   
        //creates a List from the specified Array   
        return Lists.newArrayList(arr);   
    }   
}  

Array: [One, Two, Three, Four, Five]
List: [One, Two, Three, Four, Five]

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