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One-liner ArrayList init

Emma Brown
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#java #programming
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Tired of verbose list initialization? Discover a cleaner, more concise approach to populating your collections. Unlock elegance and efficiency!

Is `Arrays.asList()` the most efficient way to initialize an `ArrayList` for testing, or are there better alternatives?

Solution in a Nutshell

One-liner ArrayList Initialization in Java

Java offers several concise ways to initialize ArrayLists. For Spring Boot developers, understanding efficient initialization is crucial for clean code.

Method 1: Using Arrays.asList() (Immutable)

This is quickest but creates an immutable list; you can't add or remove elements.

List<String> list = Arrays.asList("apple", "banana", "cherry");

Method 2: Using List.of() (Java 9+) (Immutable)

Similar to Arrays.asList(), but generally preferred for its clarity. Also immutable.

List<String> list = List.of("apple", "banana", "cherry");

Method 3: Constructor with Collection (Mutable)

For mutable lists (allowing additions/removals), use the constructor taking a Collection.

List<String> list = new ArrayList<>(Arrays.asList("apple", "banana", "cherry"));

Method 4: Using streams (Java 8+) (Mutable)

Ideal for initializing from other data sources.

List<String> list = Stream.of("apple", "banana", "cherry").collect(Collectors.toList());

Recommendation: For simple, fixed-size lists, List.of() is the cleanest and most preferred approach. For mutable lists, use the constructor with Arrays.asList() as the argument. Avoid modifying lists created with Arrays.asList() or List.of() to prevent UnsupportedOperationException.