Uses of custom annotations, how to

Question

Suppose you set up a custom annotation

public @interface ThreadSafe {
}

To indicate to the reader of your code that classes or methods are in fact Thread Safe

Other then a variant of a comment, how else can these types of custom annotations be used?

Answer 1

If you're just asking about potential applications of such an annotation, here's a few off the top of my head...

• Reflective code might take advantage of the thread-safety of annotated methods. For example, Guava's EventBus uses an @AllowConcurrentEvents annotation as a hint for its EventBus framework.
• Static analysis tools can use annotations as hints -- either that a method should have a certain property, or that users of this method can assume a certain property. For example, a static analysis tool might perform extra checks on methods annotated @ThreadSafe to make sure they are, in fact, thread safe.
• You could design preprocessors that might identify optimization opportunities that are only available because a specific method is thread-safe.

Answer 2

Such annotations can bring information that could be used to improve the efficiency of algorithms. The RandomAccess interface is used for this purpose.