What Is Abstract Class Data Type?


Larry Thompson

What Is Abstract Class Data Type?

An abstract class data type is a concept in object-oriented programming that allows for the creation of classes that cannot be instantiated directly, but can serve as a base for other classes. It provides a way to define common characteristics and behaviors that subclasses can inherit and customize.

Understanding Abstract Classes

An abstract class is declared using the abstract keyword. It serves as a blueprint or template for creating derived classes. Unlike regular classes, you cannot create objects of an abstract class directly.


abstract class Animal {
    // Common characteristics and behaviors
    abstract void sound();
    abstract void eat();

class Dog extends Animal {
    // Implementing abstract methods
    void sound() {

    void eat() {
        System.println("Eating bones");

In the above example, we have an abstract class named Animal with two abstract methods: sound() and eat(). These methods do not have any implementation in the abstract class. The Dog class extends the Animal class and provides implementations for the abstract methods.

The Purpose of Abstract Classes

The purpose of using an abstract class is to define common functionality that can be shared among multiple related classes. It allows you to enforce certain methods that must be implemented by all subclasses, ensuring consistency in behavior.

abstract class Shape {
    // Common method
    abstract double calculateArea();

    // Concrete method
    double calculatePerimeter() {
        return 0.0;

class Circle extends Shape {
    double radius;

    double calculateArea() {
        return Math.PI * Math.pow(radius, 2);

    double calculatePerimeter() {
        return 2 * Math.PI * radius;

class Rectangle extends Shape {
    double length;
    double width;

    double calculateArea() {
        return length * width;

In the above example, the abstract class Shape defines a common method calculateArea() that must be implemented by all subclasses. It also provides a concrete method calculatePerimeter() with a default implementation that can be optionally overridden.

Key Points to Remember

  • An abstract class cannot be instantiated directly.
  • An abstract class can have both abstract and non-abstract methods.
  • A subclass must provide implementations for all abstract methods of its superclass.
  • An abstract class can have instance variables and constructors.
  • You can create references of an abstract class type, but they must point to objects of concrete subclasses.
Animal animal = new Dog();
animal.sound(); // Outputs "Woof!"
animal.eat();   // Outputs "Eating bones"


The concept of abstract classes in object-oriented programming allows for the creation of common characteristics and behaviors that subclasses can inherit and customize. It promotes code reusability, consistency, and modularity in software development projects. By understanding this concept, you can design more flexible and maintainable code structures.

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