How to convert an array to a List in Java?

The Problem

I don’t know how to convert an array to a List in Java.

The Solution

In Java, you can convert an array to a List in several ways, depending on your requirements and the Java version you are using.

We’ll demonstrate how to use the following:

• The Arrays.asList() method
• The ArrayList constructor
• The Collections.addAll() method
• The Java 8+ Stream API

Using Arrays.asList()

The Arrays.asList() method is the simplest way to convert an array to a List.

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

public class Main {
    public static void main(String[] args) {
        String[] array = {"Apple", "Banana", "Cherry"};
        List<String> list = Arrays.asList(array);
        System.out.println("List: " + list);
    }
}

Lists returned by Arrays.asList() are fixed-size, meaning list elements cannot be added or removed. Attempts to add or remove list elements throw an UnsupportedOperationException.

Using ArrayList

The result of the Arrays.asList() method can then be passed to the ArrayList constructor to create a mutable list.

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

public class Main {
    public static void main(String[] args) {
        String[] array = {"Apple", "Banana", "Cherry"};

        List<String> list = new ArrayList<>(Arrays.asList(array));

        list.add("Berry"); // This adds a new element to the list
        System.out.println("List: " + list);
    }
}

You can add and remove elements to mutable lists like the one created by the ArrayList constructor above.

Using Collections.addAll()

The Collections.addAll() method can be used to convert an array to a List by adding the array elements to an existing list.

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        String[] array = {"Cherry"};
        List<String> fruitsList = new ArrayList<>(Arrays.asList("Apple", "Banana"));

        Collections.addAll(fruitsList, array); // This adds the array with a "Cherry" element to the list of fruits
        System.out.println("List: " + fruitsList);
    }
}

This outputs the following:

List: [Apple, Banana, Cherry]

Using Java Streams

If you are using Java 8 or later, you can use the Stream API to convert an array to a List.

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        String[] array = {"Apple", "Banana", "Cherry"};
        List<String> list = Arrays.stream(array).collect(Collectors.toList());
        System.out.println("List: " + list);
    }
}

This method is useful if you need to perform additional stream operations, such as filtering or mapping, during the conversion.

For example, you can convert an array to a list and filter out elements that start with a specific letter:

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        String[] array = {"Apple", "Banana", "Berry", "Cherry"};
        List<String> list = Arrays.stream(array)
                                  .filter(s -> s.startsWith("B"))
                                  .collect(Collectors.toList());
        System.out.println("List: " + list);
    }
}

This outputs the following:

List: [Banana, Berry]