A sub-class has no access to private instance variables of its super class.

Question

BlackTom AI · Accepted Answer

Private members are accessible only within the class in which they are declared; subclasses cannot directly access them.

1) Relevant knowledge points and concepts
- Access modifiers (private, protected, public) control visibility of class members.
- In mainstream OOP languages (Java, C++, C#), private instance variables are hidden from subclasses; they are part of the superclass's encapsulation.
- Subclasses can use public or protected methods (getters/setters) of the superclass to interact with those variables, but not reference them directly.
- Some languages (e.g., Python) use naming conventions or name mangling rather than strict access control; reflection or special mechanisms can bypass visibility but these are exceptions, not the rule.

2) Step-by-step reasoning
- Superclass declares a private instance variable. This places that variable in the superclass's private namespace.
- When a subclass is declared, it inherits the object layout and the existence of that variable, but the language enforces that code written in the subclass cannot directly name or access that private member.
- Attempting to reference the private variable in subclass code triggers a compile-time error (Java/C#) or access-denied semantics (C++).
- Therefore, by definition and language enforcement, the subclass has no access to the private instance variable.

3) Intermediate "steps" (illustrative code behavior)
- Java example:
  class Super { private int x; }
  class Sub extends Super { void m() { int y = x; } } // compile error: x has private access in Super
- C# / C++ behave similarly: direct reference to private member from derived class is disallowed.

4) Why the correct answer is correct
- The statement asserts that a sub-class has no access to private instance variables of its super class. This matches the standard semantics of private visibility in object-oriented languages: private means "accessible only within the declaring class." Hence the statement is true.

5) Why the other option (False) is incorrect
- Claiming False would mean subclasses can access private members directly. That contradicts language-defined visibility rules and would allow breaking encapsulation; it is therefore incorrect. (Exceptions like reflection, friend declarations, or Python's conventions are special cases, not the general rule implied by the statement.)

Conclusion: The correct answer is True, which matches the provided answer.

A sub-class has no access to private instance variables of its super class.判断题

类似问题

When using inheritance, fields of the superclass are typically declared as:

The protected access modifier allows access from:

____________ access modifier is only visible in parent and child class, but not in other packages.

____________ access modifier is only visible in parent and child class, but not in other packages.

Choose the correct option to be included for the <access-modifier>

_______ is the access specifier to make a class member accessible only within the same class.

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