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Private method overiding  RSS feed

 
Ranch Hand
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Hi All,

OCAJP - 1 book assessment test has below program. I did not understand how could parent access its private method when parent reference instantiated child object.



ouput is deer childCH false.

I am expecting deer childCH true. According to run-time polymorphism, child class hasHorns has to be invoked, right? Please let me know. Thanks.
 
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Private methods are not overridden -- no polymorphism.

Henry
 
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Please supply more details of the book: is it by Boyarsky and Selikoff?

Please follow the execution through the constructors;-
  • 1: ChildCH constructor calls no‑arguments superclass constructor.
  • 2: ConstructorHierarchy constructor calls its superclass' constructor (=Object()).
  • 3: Object() completes and control passes back to ConstructorHierarchy() which prints “deer”
  • 4: ConstructorHierarchy() ocmpletes and control passes to ChildCH() which prints “ChildCH”
  • 5: Line 21 completes.
  • Now,, you can access the private method because you are inside the same class. The hasHorns() method is not inherited by ChildCH; it exists only in ConstructorHierarchy. Since there is no polymorphism involved, the type of the method is bound statically at compile‑time on the declared type of the variable, i.e. ConstructorHierarchy. The method with a similar name in the subclass is not an overriding method.

    Private methods are not inherited. The method in the subclass is a new method completely unrelated to the superclass' method. So it is not called polymorphicaally and the superclass method prints false.
     
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