Question

@Deprecated public class Betamax { ... } 

In the above example, what effect does the @Deprecated have? Is it purely documentation? Or does it change something about how the compiler treats this class?

Answer 1

The compiler enforces (as in checks and croaks on) some annotations (like @Override).

But the most useful part is that libraries can provide their own annotations (like @Entity or @PersistenceAware), of which the Java language (JDK core) does not know anything. This is kind of like adding domain-specific syntactic sugar right into the language.

@Deprecated is for documentation. It also creates compiler warnings when you use a deprecated method (or class), just like the old JavaDoc @deprecated tag.