What is Double Brace initialization in Java?

Question

What is Double Brace initialization syntax ({{ ... }}) in Java?

Answer 1

As pointed out by @Lukas Eder double braces initialization of collections must be avoided.

It creates an anonymous inner class, and since all internal classes keep a reference to the parent instance it can - and 99% likely will - prevent garbage collection if these collection objects are referenced by more objects than just the declaring one.

Java 9 has introduced convenience methods List.of, Set.of, and Map.of, which should be used instead. They're faster and more efficient than the double-brace initializer.