Fast and reliable way to find out if a source code file implements an interface

Question

Given a java source code file, what is a fast and reliable way to find out if it implements a given interface?

A reliable way would be to parse the file into a syntax tr

Answer 1

What would you do?

I would compile the source code of the class and the interface, load both using Class.forName(), and use Class.isAssignableFrom to test if the class is a subtype of the interface.

Relatively fast, totally reliable ... assuming that the source code is compilable.

Note that this can all be done at runtime, and if you use a throw-away instance of a properly implemented custom classloader to do the loading, you can avoid polluting your JVM with dubious classes.

Answer 2

I would say that parsing a source code file is both, fast and reliable. But "fast" is such a vague notion that it really depends, I guess. I wouldn't expect too much overhead when compared to scanning the source file for occurrences of the words "implements", though -- thus if the latter is fine for you, I'd assume the former should be acceptable too?

The javax.tools.* API would be a good entrance point to get started; however, there are also a number of (open source) source code parsers for Java out there.

Also, here is an introductory blog post on Oracle's websites.