Class methods (static methods) are methods that don't work on an object, but that are for the whole class.
When you call a class method on an instance, the code looks as if it is a regular non-static method that works on the object that you call it on. But that's not really the case, so code written in that way will look confusing.
In my opinion, it should not have been allowed at all to call static methods on instances - I regard it as a mistake in the design of the
Java programming language that this is possible.