Find Self-Referential Code in IntelliJ - intellij-idea

Question

In IntelliJ when code is not used anywhere it will be "grayed out." Is there any way to see if a set of classes aren't used anywhere?
I have this set of classes with references to each other so IntelliJ is counting this set of classes as being used. In this case I know the code is useless but it would be nice to have the ability to automatically detect this sort of thing. The logic to do this isn't amazingly difficult... Does anyone know if this is possible in IntelliJ?

Answer 1

This "greyed out" mark simply reflects declaration usages in other source code files or framework configuration files. Declaration usage search cannot detect orphan clusters of classes as these classes are formally referenced.
There is a technique, that may help here: define some root set of entry points (main() methods, web.xml declarations, etc) and trace all the references, effectively building a graph of used classes/methods. Once graph is completed, you can treat unvisited classes as dead code. Pretty similar to what Java garbage collector does during young gen collection. It is quite difficult and resource consuming for on-the-fly code analysis, so Intellij has it implemented as a separate inspection one can run manually.
To demonstrate it let's create a fresh project containing the following code:
public class Main {
public static void main(String[] args) {
System.out.println(new Used());
}
}
class Used {}
class ObviouslyUnused {}
class TrickyUnused1 {
TrickyUnused1() {
System.out.println(new TrickyUnused2());
}
}
class TrickyUnused2 {
TrickyUnused2() {
System.out.println(new TrickyUnused1());
}
}
In the editor we can see, that only ObvoiuslyUnused is greyed out. Let's run an "Unused declaration" inspection:
and here we go, inspections shows, that our unused self-referenced class cluster is not reachable:
You should be aware, though, that there are always means of referencing code in implicit ways: reflection, native calls, runtime code generation, SPI implementations, references from framework configuration files, etc. So no static anlisys tool can be 100% accurate when detecting dead code.