Why can I invoke a private method on an instance of the sub-class when it shouldn't be visible to the instance?

Question

This question is similar to Why can a "private" method be accessed from a different instance?

I am convinced with the answer there. The code should run. However when I change the code to be like this

class Horse extends Animals{
}

public class Animals {

    private void eat(){
        System.out.println("Generic Eating");
    }

    public static void main(String[] args){
        Animals h = new Horse();
        h.eat();
    }

}

when I try to use polymorphism to invoke the private method eat() on the Sub-class Horse it works and calls the method of the parent class.

• doesn't java dynamically call the instance specific method of the class?
• shouldn't this throw a runtime exception?
• does this mean the method is actually inherited but not normally accessible?

Answer 1

In your example, a Horse is an Animal . So yes, a Horse has one method called eat , because every Animal has one such method, and every Horse is an Animal .

The method eat was defined by the class Animal , and is a private method in that class. Which means it can only be accessed from within other methods defined in the Animal class, and nothing else. No super-/sub-classes, no wrappers, no containers, no nothing. Not even a Horse which, even though it is an Animal , it is not Animal itself.

So your example works in the way it was expected to work.

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As a final note, answering specifically to the question in the "title",

Why can I invoke a private method on an instance of the sub-class when it shouldn't be visible to the instance?

The only thing that matters is from where you are invoking that private method. You are invoking it from within the class in which it was defined. Therefore it is accessible.