Abstract Class Overview in Programming

Questions and Answers

What is an abstract class?

A class which cannot be instantiated. It may or may not contain one or more abstract methods.

What is an abstract method?

A template for a method that concrete subclasses must implement.

Why use an abstract class?

To categorize objects that share common behavior but have different implementations.

Give an example of an abstract class.

An abstract class 'Shape' with a method 'area'. Signup and view all the answers

How do you declare an abstract class and an abstract method?

Eg.abstract public class Shape { public abstract double getArea(); } Signup and view all the answers

What keyword allows a subclass to inherit an abstract class?

'extends' Signup and view all the answers

Can you instantiate an abstract class?

False Signup and view all the answers

A class may be declared abstract even if it has no abstract methods.

True Signup and view all the answers

Provide a summary of an abstract class.

An abstract class cannot be instantiated and is used to create inheriting subclasses. It defines methods that must be implemented and provides a common interface. Signup and view all the answers

Study Notes

Abstract Class Overview

An abstract class cannot be instantiated directly.
It can contain abstract methods that must be implemented by subclasses.
Abstract classes are useful for defining a common interface among related objects.

Abstract Method

An abstract method serves as a "template" that concrete subclasses must implement.
Ensures that all subclasses adhere to a specified method structure.

Purpose of Abstract Classes

Abstract classes facilitate a category of objects sharing common behavior while allowing specific implementation details to vary.
They are instrumental in designing systems that require polymorphism and code reusability.

Example of an Abstract Class

"Shape" is an example of an abstract class.
It may contain an abstract method like "area," which is implemented differently by subclasses such as Circle, Square, and Rectangle.

Declaration of Abstract Classes and Methods

Abstract classes are declared using the "abstract" keyword.

An example declaration:

abstract public class Shape {
    public abstract double getArea();
}

Inheritance of Abstract Classes

Subclasses use the "extends" keyword to inherit from an abstract class.

For example:

public class Circle extends Shape {
    private double radius;

    public Circle(double r) {
        radius = r;
    }

    public double getArea() {
        return Math.PI * radius * radius;
    }
}

Instantiation of Abstract Classes

Abstract classes cannot be instantiated; only concrete subclasses can be created.

Abstract Class Without Abstract Methods

A class can be declared abstract without containing any abstract methods.
This prevents the class from being instantiated, useful in specific design patterns.

Summary of Abstract Classes

Abstract classes define methods and provide a common interface for their subclasses.
They are instrumental in creating a structure for polymorphic behavior in object-oriented programming.

Description

This quiz covers the essential concepts of abstract classes and methods in programming. Learn about their purpose, declaration, and how they facilitate code reusability and polymorphism using examples such as the Shape class. Test your knowledge on this fundamental object-oriented programming topic.