getClass() and instanceof

Question about the task

Under discussion

"The equals method should check whether the passed object is a Solution object." Per the stated condition, why does code that uses getClass() check not pass but the instanceof check does? Strictly speaking the instanceof operator is not checking to see if the passed object is a Solution object, but if it is an instance of it, which means subclasses of Solution would be as valid as their parent. I understand this may be a desired property, but

getClass() != o.getClass()

should also pass right?

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Gellert Varga

Level 23 , Szekesfehervar, Hungary

6 February 2021, 19:07

I think not. The equals() method with the "instanceof" operator will return true even if the passed object a child of the Solution. The equals() method - if inside you are checking just with with the getClass() method - will return true only if the passed object was created from the Solution Class. (But I don't know this specific task yet - so i'm sorry if i said just something bullshit...)

Adrian

Level 27 , Spanish Town, Jamaica

7 February 2021, 01:08

Right, there are, I found out entire schools of thought surrounding this, even the IDE lets you know that it will break the equals contract in the name of allowing subclasses to pass the validity check. It seems to me this comes down to how the coder defines equality for his or her objects, that said if the condition guideline is to make sure that only Solution objects validate, then I think the getClass check is a valid alternative if not technically the most suitable. (since "Solution object" and "instances of Solution" are different things. Also, before you get to this specific task you will see Codegym uses the .getClass implementation in tasks they wrote, so it seems strange that code that uses it here doesn't validate

Nouser

Level 36 , Germany

7 February 2021, 11:35

Don't worry about that to much. I had the same issue at that time. One task verified using instanceof, the next didn't. I just think different people wrote the validation for that tasks and each one had different way to write the equals method. instanceof just has the check for null included but is less strict when it comes to inheritance. That may not be wanted in every case...