![]() In this article on how to initialize an ArrayList in Java, we have seen different approaches to initialize and create an ArrayList. The Guava library provides different methods to create immutable lists:įor example, if we want to initialize an ArrayList in Java with ImmutableList.of, we can do it as follows: List fruits = ImmutableList.of("apple", "orange", "banana") Īnother method provided by the Guava library to initialize a list in Java is pyOf(), which returns a list with the specified elements: ImmutableList fruits = pyOf(Arrays.asList("apple", "orange", "banana")) Īs a note, pyOf returns null if any of the elements are null. The Collections.unmodifiableList() method returns an unmodifiable list from a series of elements: List fruits = Collections.unmodifiableList(Arrays.asList("apple", "orange", "banana")) Īnother method provided by the Java Collections API is singletonList(), which returns an unmodifiable list with a single element: List fruits = Collections.singletonList("apple") Using the Guava libraryĪnother approach to initializing an ArrayList in Java is using the Guava library. Through the Collections class, we can use different methods to create a list. ![]() List fruits = Stream.of("apple", "orange", "banana").collect(Collectors.toCollection(ArrayList::new)) The toCollection() method creates a collection using a Collector and passes a new instance of ArrayList to it. Different ways to initialize an array in C++ Arrays: A simple way is to represent the linear relationship between the elements represented using sequential. List fruits = Stream.of("apple", "orange", "banana").collect(Collectors.toList()) The toList() method returns a new list through the Collector interface with the values passed to the Stream. With the introduction of Java Streams, we can create and initialize an ArrayList using the toList() and toCollection() methods. List fruits = List.of("apple", "orange", "banana") Using the Java Stream API However, we need to note that we cannot use the add() operation. We can use the static method List.of() to construct unmodifiable lists. Using List.of from Java 9 to initialize an ArrayList in Java We can use the ArrayList constructor and pass the elements we want to initialize through asList(): ArrayList fruits = new ArrayList( Arrays.asList("apple", "orange", "banana") ) Using Arrays.asList() to initialize an ArrayList from an Array There are multiple ways to do it, and in this article, we will cover the most frequent and common ones. Let’s see how to initialize an ArrayList in Java according to our needs. ![]() One of my recommended course to all Java programmers.Arraylist, collection, immutableList, singletonList, stream, unmodifiableList You can read more about shall and deep cloning in Java on The Complete Java Masterclass course on Udemy. This will be the shallow copy so beware, any change made on an object will reflect in both the list. If you want to convert this fixed length List into a proper ArrayList, LinkedList or Vector any other Collection class you can always use the copy constructor provided by the Collection interface, which allows you to pass a collection while creating ArrayList or LinkedList and all elements from the source collection will be copied over to the new List. Nevertheless its clean solution for creating and initializing List in Java in one line, quite useful for testing purposes. It's kind of fixed length Lists which doesn't support the addition and removal of elements. java: 32 )Īs shown in the above example it's important to remember that List returned by Arrays.asList() can not be used as a regular List for further adding or removing elements. This also throws Įxception in thread "main" java. List returned by Arrays.asList is fixed size initializing list with an array in java * Which means adding and deleting elements from the * fixed-size List and you can not change its size. * from Array but List returned by this method is a * Arrays.asList() method is used to initialize a List * How to create and initialize List in the same line,
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