How to quickly and conveniently create a one element arraylist

Quick ways to generate singleton lists

Immutable list using Collections.singletonList()

Need a list that's set in stone? Use the Collections.singletonList() method for a quick, immutable list:

List<String> immutableList = Collections.singletonList("immutableElement");
// That's it. Don't even think of trying to change it. Seriously.
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Java 9 List.of() method for immutable list

In Java 9 and onwards, you can use the List.of() method for a nice one-item immutable list:

List<String> oneElemImmutable = List.of("oneElement");
// Immutable as a diamond. Shiny!
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Create list using Stream API

Java's Stream API allows you to create collections in a more functional style:

List<String> fromStream = Stream.of("streamedElement").collect(Collectors.toList());
// Stream it like Netflix.
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Google's Guava library approach

The Guava library from Google gives us Lists.newArrayList(), an elegant method to create a mutable list:

List<String> guavaList = Lists.newArrayList("guavaElement");
// Who doesn't like Guava, right?
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Digging deeper: Other singleton collection options

Stream API beyond just Lists

We are not only restricted to Lists. Say hello to Sets! A Set with single element:

Set<String> singleElementSet = Stream.of("uniqueElement").collect(Collectors.toSet());
// Feels lonely? Make it a set. There can only be one!
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Multiplying your one element

For those rare situations where you need multiple copies of the same element in a list, Java has you covered with Collections.nCopies:

List<String> identicalElements = new ArrayList<>(Collections.nCopies(5, "sameElement"));
// It's like a glitch in the Matrix.
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Mutable, Immutable or fixed-size?

Different methods yield different types of collections:

• Collections.singletonList() generates an immutable list.
• Arrays.asList() produces a fixed-size list.
• Wrapping with new ArrayList<>() bestows mutability.

Watch your step!

IDE might not be your savior

Your IDE might be a lifesaver, but it won't always warn you about single-element asList calls. Stick to Collections.singletonList() for clarity.

Respect immutability

Caught yourself transforming asList() into new ArrayList<>()? Stop right there if you truly respect immutability.

A fair warning about type safety

Java Generics and <> exist for a reason. Harness their potential for type safety:

List<Integer> singleIntList = new ArrayList<>(Collections.singletonList(42));
// It's the answer to life, universe, and everything!
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Pro tips for power users

Third-party libraries: An ocean of opportunities

Java's standard library is vast, but third-party libraries like Guava can serve as a treasure trove of handy utilities.

Battling overloads

Methods such as Arrays.asList() and List.of() are loaded with overloads. Know their role and use them wisely, especially for single-element collections.

The ever-evolving Java

Keep a lookout for the upcoming enhancements in Java. Singleton collections might get even simpler and faster.