Question

What does a subclass inherit from its superclass?

Short answer

Answer: In object-oriented programming, a subclass can inherit the following properties and methods from its superclass: 1. Public properties: These are the variables defined as public in the superclass and can be accessed by the subclass. 2. Protected properties: These are the variables declared as protected in the superclass, accessible within the subclass and superclass only. 3. Public methods: Functions defined as public in the superclass are inherited and can be accessed within the subclass. 4. Protected methods: Functions declared as protected in the superclass, accessible within the subclass and superclass only. However, a subclass does not inherit private properties and private methods from its superclass, as they are exclusive to the superclass. For example, in Java, if the `Employee` class (subclass) inherits the `Person` class (superclass), it will have access to public/protected properties like `name` and `age`, and public/protected methods like `greet()` and `displayAge()`.

Step-by-step solution

Introduction to Inheritance

Inheritance is a fundamental concept in object-oriented programming (OOP). It allows a new class (called subclass) to inherit properties and methods from an existing class (called superclass). This helps in reusing the code and creating a relationship between classes.

Understanding Superclass and Subclass

A superclass is an existing class from which other classes can inherit properties and methods. On the other hand, a subclass is a new class that is derived from an existing class (superclass). The subclass can have its own specific properties and methods in addition to the inherited ones.

What Does a Subclass Inherit from Its Superclass?

A subclass inherits the following from its superclass: 1. **Public properties:** All the public properties (variables) defined in the superclass are accessible and inherited by the subclass. 2. **Protected properties:** Properties declared as protected in the superclass can also be inherited by the subclass. However, they cannot be accessed outside the subclass or superclass. 3. **Public methods:** All the public methods (functions) defined in the superclass are accessible and inherited by the subclass. 4. **Protected methods:** Methods declared as protected in the superclass can also be inherited by the subclass. However, they cannot be accessed outside the subclass or superclass.

What a Subclass Does Not Inherit

A subclass does not inherit the following from its superclass: 1. **Private properties:** Private properties defined in the superclass are not accessible to the subclass. They are exclusive to the superclass only. 2. **Private methods:** Similarly, private methods defined in the superclass are not accessible to the subclass. They can only be used within the superclass.

Example of Inheritance in Java

Let's consider an example using Java programming language to illustrate inheritance: ``` public class Person { public String name; protected int age; public void greet() { System.out.println("Hello, " + name); } protected void displayAge() { System.out.println("Age: " + age); } } public class Employee extends Person { public String company; public void work() { System.out.println(name + " works at " + company); } } ``` In this example, the `Employee` class is the subclass, and it inherits the `Person` class's properties and methods. The `Employee` class has access to the public properties `name` and the public method `greet()`. It can also access the protected property `age` and the protected method `displayAge()`.

Key concepts

Inheritance

Inheritance is a powerful feature in object-oriented programming that allows a class to derive properties and behaviors from another class. This concept helps developers write cleaner and more organized code. Without duplicating code, a subclass can reuse and extend the functionalities provided by the superclass.

By using inheritance, we establish a hierarchical relationship between classes, allowing for more modular and easier to maintain codebases. This is especially beneficial in large projects, where it aids in updating and fixing bugs, as a change in the superclass automatically affects all its subclasses.

Subclass and Superclass

In object-oriented programming, the superclass is the original class from which other classes derive. A subclass, on the other hand, is a new class that extends the functionality and properties of the superclass. Understanding these roles is crucial in utilizing inheritance effectively.

Subclasses not only inherit methods and properties from the superclass, but they can also add new ones or override existing ones to tailor their functionalities. This allows programmers to create versatile and diverse object hierarchies, where complex behaviors emerge from simple, well-defined building blocks.

• Superclass: Provides the base functionality and characteristics.
• Subclass: Extends or customizes the base class, adding its own features and adjustments.

Java Example

Let’s delve into a practical Java example to better understand how inheritance works. Below, the `Person` class is a superclass, and `Employee` is its subclass: ```java public class Person { public String name; protected int age; public void greet() { System.out.println("Hello, " + name); } protected void displayAge() { System.out.println("Age: " + age); } } public class Employee extends Person { public String company; public void work() { System.out.println(name + " works at " + company); } } ``` This Java snippet shows `Employee` inheriting both public and protected elements from `Person`. The `name` property and `greet()` method are public, meaning they are available to any class. Meanwhile, the `age` property and `displayAge()` method are protected, accessible in `Person`, `Employee`, and any subclass.

The `Employee` class can also have additional methods like `work()`, showcasing how subclasses can introduce new features while retaining access to the superclass's components.

Public and Protected Properties

Inheritance in Java doesn't just mean reusing code; it's also about managing accessibility. Properties and methods in Java can be defined with different access levels, with `public` and `protected` being two critical ones in inheritance:

• Public Properties: These are accessible from any other class. In the `Person` example, the `name` property is public, thus, accessible to all, including outside the inheritance hierarchy.
• Protected Properties: These are visible to the superclass and its subclasses, but not to classes outside the hierarchy. `age` in the `Person` class is protected, allowing `Employee` to access it but not other unrelated classes.

These properties enable you to control the exposure of your class members appropriately, maintaining encapsulation and integrity while allowing flexible inheritance. This nuanced control helps in designing robust software architectures.