Inheritance

Object-oriented Programming Features

• Focus: Inheritance

Inheritance

• Allows child classes to inherit attributes and operations from parent classes.

  • Attributes: Fields and properties inherited from the parent class.

  • Operations: Methods inherited and/or redefined from the parent class.

• Aims for code reusability, enabling common properties/functions to be extended rather than rewritten.

Types of Inheritance

• Terminology:

  • Base class / Derived class: Parent-child relationship in class structure.

  • Interfaces: Derived interfaces implement base interfaces.

Benefits of Inheritance

• Extensibility and reusability of code.

• Provides abstraction.

• Eliminates redundant code.

• Promotes "is-a" relationships:

  • Example: Dog is-an Animal.

• Avoids "has-a" relationships:

  • Example: Dog has-a Name (not a true inheritance relationship).

Inheritance Examples

• Class Structure:

  • Employee class with fields: Name, Address, Company.

  • Student class with fields: Name, Address, School, Salary.

  • Derived classes share common properties and extend functionality.

Types of Inheritance in Java

• Single Inheritance: One parent, one child.

• Multiple Inheritance: Not supported directly in Java but can be achieved through interfaces.

• Multilevel Inheritance: Child classes derive from other child classes.

• Hierarchical Inheritance: Multiple subclasses from the same parent.

Class Hierarchies

• General characteristics defined at higher levels, specific characteristics at lower levels.

Inheritance in Java

• A class can inherit from one base class while implementing multiple interfaces:

  • Syntax: public class B extends A implements IX, IY, IZ.

Defining Inheritance Syntax

• Use super keyword in derived class constructors to call base class constructors.

• Example syntax: public class Circle extends Shape {...}

Simple Inheritance Example

• Mammal Class:

  • Contains age attribute, Sleep method.

• Dog Class:

  • Inherits Mammal, adds breed attribute, WagTail method.

Adding Functionality in Subclasses

• Subclasses inherit data members and methods of the superclass.

• Can add additional members or methods to enhance functionality.

UML Diagrams Examples

• Rectangle Class - demonstrates attributes and methods in UML format.

• Box Class - inherits from Rectangle, adds 3D dimensional functionalities.

Important Aspects of Inheritance

• Java does not support multiple inheritance; constructors are not inherited.

• Inheritance is a transitive relation.

Important Features of Inheritance

• Derived classes extend base classes and add new members but cannot remove inherited ones.

Inheritance and Accessibility

• Access levels define what can be accessed in subclasses:

  • Protected and public members can be accessed, private members cannot.

Object Class in Java

• All classes inherit from Object class implicitly.

  • It contains fundamental methods including toString().

Understanding Polymorphism

• Polymorphism allows objects to take on multiple forms.

  • Example: Using a subclass as its parent class type.

  • Late binding is used to determine method calls at runtime.

Polymorphism Implementation

• Example demonstrates how methods are called based on object type at runtime.