Initialize List with Values in Java

In this tutorial, we’ll learn different ways to initialize List, ArrayList and LinkedList with values in single line in Java.

Java 8 or earlier

List

List<String> strings = Arrays.asList("foo", "bar", "baz");

or if you already have an Array

String[] array = { "foo", "bar", "baz" };
List<String> strings = new LinkedList<>(Arrays.asList(array));

This will give you a List which is backed by an Array. Note that this List is immutable. That means if you try to add or remove any element from the List, It will throw java.lang.UnsupportedOperationException exception.

List is mostly useful when you just want to populate a List and iterate it.

If you want to create a mutable List where you can add or remove elements. Initialize an ArrayList or LinkedList instead.

ArrayList

List<String> strings = new ArrayList<>(Arrays.asList("foo", "bar"));
strings.add("baz");

You can also use Collections.addAll() static method to add values to ArrayList

List<String> strings = new ArrayList<String>();
Collections.addAll(strings,"foo", "bar", "baz");

Another way is to making an anonymous inner class with an instance initializer. This is also known as an double brace initialization. However that looks like an overkill to create a inner class just to create an ArrayList.

List<String> strings = new ArrayList<String>() {
  {
    add("A");
    add("B");
    add("C");
  }
};

LinkedList

LinkedList can be initialized similarly as an ArrayList using above three examples.

Java 9 or later

List.of() is added in Java 9 which can be used to initialize a List with values.

List<String> strings = List.of("foo", "bar", "baz");

With Java 10 or later, this can be even more shortened with the var keyword.

var strings = List.of("foo", "bar", "baz");

Also we can define ArrayList:

List<String> strings = new ArrayList<>(List.of("foo", "bar"));
strings.add("baz");

Using Streams

You can also use Stream which is more flexible:

Stream<String> strings = Stream.of("foo", "bar", "baz");

You can concatenate Streams:

Stream<String> strings = Stream.concat(Stream.of("foo", "bar"),
                                       Stream.of("baz", "qux"));

Or you can go from a Stream to a List:

List<String> strings = Stream.of("foo", "bar", "baz").collect(Collectors.toList());

Or you can even go from a String to an ArrayList:

List<String> strings = Stream.of("foo", "bar").collect(Collectors.toCollection(ArrayList::new));
strings.add("baz");