Question

When a class member is declared as protected, what code may access it?

Short answer

Answer: A class member declared as protected can be accessed by the containing class itself, any class that inherits from the containing class (deriving classes or subclasses), and in C++: classes within the same package.

Step-by-step solution

Understand Access Specifiers

Access specifiers define the level of access granted to class members (like attributes and methods) in object-oriented programming languages like C++, Java and C#. There are three types of access specifiers: public, private, and protected.

Define 'Protected' Access Specifier

Protected is an access specifier that allows class members to be accessed within the containing class, as well as by classes which inherit from the containing class, but not by other code outside of these two scenarios.

When can Protected Class Members be accessed?

Class members declared as 'protected' can be accessed by: 1. The containing class itself. 2. Any class that inherits from the containing class (deriving classes or subclasses). 3. In C++: Classes within the same package are allowed access to protected class members (this is not applicable to languages like Java and C#). Code outside of these specific scenarios will not be able to directly access protected class members.

Key concepts

Object-Oriented Programming

Object-Oriented Programming (OOP) is a programming paradigm that uses "objects" to design software. Objects are instances of classes, which can encapsulate data and the functions that manipulate this data. This approach allows for modular and reusable code, making it easier to manage larger codebases.
OOP principles include:

• Encapsulation: Bundling data and methods that operate on that data within one unit, like a class.
• Abstraction: Hiding complex implementation details and showing only the essential features.
• Inheritance: Allowing new classes to be formed using properties and behaviors (methods) of existing classes.
• Polymorphism: Enabling objects to be treated as instances of their parent class, yet behave differently based on their actual class type.

One major benefit of OOP is its ability to model real-world entities more accurately than procedural programming, offering a structure that teams can work on collaboratively and efficiently.

Java Access Modifiers

In Java, access modifiers are keywords that set the accessibility of classes, methods, and other members. They are crucial in object-oriented programming as they help control the visibility and accessibility of class components.
Java has four main types of access modifiers:

• Public: Members are accessible from any other class.
• Private: Members are accessible only within the same class.
• Protected: Members are accessible within their own package and by subclasses.
• Default: (No keyword used) Members are accessible only within their own package.

Protected specifically enables subclasses (in the same package or located elsewhere) to access the class members while restricting access from other unrelated parts of the program. This is advantageous when developing libraries or frameworks where the internal logic needs to be accessed by extended classes but hidden from the public API.

Inheritance in Java

Inheritance is one of the core principles of object-oriented programming, particularly in Java. It allows a new class, known as the child class or subclass, to acquire properties and methods from an existing class, called the parent class or superclass.
This concept promotes code reusability and can simplify the programming model by spreading common behavior across multiple subclasses. For example, if a superclass 'Vehicle' has methods like 'accelerate' and 'brake', any subclass like 'Car' or 'Bike' can inherit and use these methods.

• Java uses the `extends` keyword to establish inheritance between classes.
• This allows subclasses to override methods from the superclass, providing specific implementations of those methods, an exercise in polymorphism.
• Constructors are not inherited, but a subclass can call a superclass constructor using `super()`.
  

Utilizing inheritance thoughtfully helps in maintaining a clean and efficient codebase by reducing redundancy and isolating changes to shared functionality in one location.