Abstraction

It is the design process of hiding the implementation and showing only the functionality (declaration) to the user.

Ways to Achieve

1. Abstract Classes (0 to 100% abstraction)
2. Interfaces (100% abstraction)

Abstract Modifier

Keyword: abstract. Applicable for methods and classes.

Abstract Method

A method prefixed with abstract, having no implementation (ends with semicolon). • Syntax: abstract [access_mod] returnType methodName(args); • Known as "Incomplete Method". • Rules:

• Cannot be private, static, or final.
• Child class is responsible for implementation.

Abstract Class

A class prefixed with abstract. • Cannot define an object (Instance) for an abstract class. • Can consist of both abstract and concrete methods. • If a class has at least one abstract method, the class must be declared abstract. • Constructor: Allowed (invoked via constructor chaining).

Implementation Rules:

1. If a class extends an abstract class, it must implement all abstract methods.
2. If it fails to do so, the subclass must also be declared abstract.

When to use Abstract Methods? • When we don't have a clear idea about implementation. • To force child classes to provide their own implementation.