Java's equivalent of arrayof()/ listof()/ setof()/ mapof() from Kotlin

Question

I was just wondering that if java has the equivalent of arrayof()/ listof()/ setof()/ mapof() like those in kotlin? If not, is there any way to work similarly? I found them

Answer 1

Java 9 brings similar methods: List#of, Set#of, Map#of with several overloaded methods to avoid calling the varargs one. In case of Map, for varargs, you have to use Map#ofEntries.

Pre Java 9, you had to use Arrays#asList as entry point to initialize List and Set:

List<String> list = Arrays.asList("hello", "world");
Set<String> set = new HashSet<>(Arrays.asList("hello", "world")); 

And if you wanted your Set to be immutable, you had to wrap it inside an immutable set from Collections#unmodifiableSet:

Set<String> set = Collections.unmodifiableSet(
    new HashSet<>(Arrays.asList("hello", "world")));

For Map, you may use a trick creating an anonymous class that extended a Map implementation, and then wrap it inside Collections#unmodifiableMap. Example:

Map<String, String> map = Collections.unmodifiableMap(
    //since it's an anonymous class, it cannot infer the
    //types from the content
    new HashMap<String, String>() {{
        put.("hello", "world");
    }})
    );