Java OOP: Classes and Objects, Inheritance

Object-Oriented Programming in Java

Classes and Objects

• A class is a blueprint for creating objects
• A class defines the properties and behaviors of an object
• An object is an instance of a class, with its own set of attributes (data) and methods (functions)

Inheritance

• Inheritance is the process of creating a new class based on an existing class
• The new class (subclass) inherits the properties and behaviors of the existing class (superclass)
• A subclass can also add new properties and behaviors or override the ones inherited from the superclass

Polymorphism

• Polymorphism is the ability of an object to take on multiple forms
• This can be achieved through method overriding or method overloading
• Method overriding: a subclass provides a specific implementation of a method already defined in its superclass
• Method overloading: multiple methods with the same name but different parameters can be defined

Encapsulation

• Encapsulation is the concept of bundling data and methods that operate on that data within a single unit (a class)
• This helps to hide the implementation details of an object from the outside world and provides a way to control access to the data

Abstraction

• Abstraction is the concept of showing only the necessary information to the outside world while hiding the implementation details
• In Java, abstraction is achieved through abstract classes and interfaces
• Abstract classes: a class that cannot be instantiated and is used as a base class for other classes
• Interfaces: a collection of abstract methods that must be implemented by any class that implements it

Composition

• Composition is the concept of creating objects from other objects
• In Java, composition is achieved through container classes that hold references to other objects

Access Modifiers

• Access modifiers (public, private, protected) control the accessibility of classes, methods, and variables
• Public: accessible from anywhere
• Private: accessible only within the same class
• Protected: accessible within the same class and its subclasses

Object-Oriented Programming in Java

Classes and Objects

• A class is a blueprint for creating objects, defining properties and behaviors
• Objects are instances of a class, with unique attributes (data) and methods (functions)

Inheritance

• Creates a new class based on an existing class (superclass)
• Subclass inherits properties and behaviors from superclass
• Subclass can add new properties and behaviors or override inherited ones

Polymorphism

• Ability of an object to take on multiple forms
• Achieved through method overriding or method overloading
• Method overriding: subclass provides a specific implementation of a superclass method
• Method overloading: multiple methods with same name but different parameters

Encapsulation

• Bundles data and methods that operate on that data within a single unit (class)
• Hides implementation details from the outside world
• Controls access to data through methods

Abstraction

• Shows only necessary information to the outside world
• Hides implementation details
• Achieved through abstract classes and interfaces
• Abstract classes: cannot be instantiated, used as base classes for others
• Interfaces: collection of abstract methods that must be implemented

Composition

• Creates objects from other objects
• Container classes hold references to other objects

Access Modifiers

• Control accessibility of classes, methods, and variables
• Public: accessible from anywhere
• Private: accessible only within the same class
• Protected: accessible within the same class and its subclasses