How compiler deals with annotations?

Question

I have some questions about working of annotations in java.

If annotations cannot be converted to bytecode then where does this information go? where does the meta-data goes? How Java Reflection uses this information?

How compiler deals with annotations?

When we say,

@Override
public void doSomething(){
}

What does a java compiler do with it?

I know that it checks the method signature so that the method should be a perfectly overridden method, but how?

Answer 1

There are three types of annotations see http://download.oracle.com/javase/6/docs/api/java/lang/annotation/RetentionPolicy.html

@Override is a special case as the compiler does additional checks.

Answer 2

@Override is a source type annotation - used to check if a particular method follows the contract of an overriden method - hence it isn't available at runtime (and therefore logically doesn't exist in the compiled bytecode).

I know that it checks the method signature so that the method should be a perfectly overridden method, but how

In the process of reading the source files and converting them to bytecode, e.g., not using reflection at all. See The Java Programming Language Compiler - javac for additional compiler information.