Question

Is there any tool that can warn me against the following sort of code:

if ( someClass.equals( someString ))

For example:

if ( myObject.getClass().equals( myClassName ))

Such a thing is legal Java (equals takes an Object) but will never evaluate to true (a class can never equal a String) so is almost certainly a bug.

I have checked Eclipse, FindBugs and PMD but none seem to support this feature?

Answer 1

Yes, IntelliJ IDEA has such an inspection that I believe is enabled by default. It flags the following:

Class<?> clazz = String.class;
if (clazz.equals("foo")) {
   //...
}

With the warning:

‘equals()’ between objects of inconvertible types.

The inspection can be enabled/disabled through Settings->Project Settings->Inspections, then under Probable Bugs check/uncheck “‘equals()’ between objects of inconvertible types.”

FindBugs also should catch this with the “EC: Call to equals() comparing different types” bug check. It can be integrated with Eclipse as it appears you are aware.

Neither is a silver bullet though; they can’t read your mind. The best you can hope for is that it will favour false positives rather than false negatives.