Abstract Class In Java

4 min read Jun 22, 2024

Abstract Class in Java

Abstract classes are a powerful feature in Java that allows you to define a blueprint for a class without providing complete implementations for all its methods. They serve as a template for other classes to inherit from, forcing them to implement specific methods while providing a common structure.

Understanding Abstract Classes

Here's a breakdown of key concepts:

Abstract Method: An abstract method is declared with the abstract keyword. It has no implementation within the abstract class. Subclasses are required to provide an implementation for these methods.
Abstract Class: A class declared with the abstract keyword. It can contain abstract methods and concrete methods (methods with implementations). An abstract class cannot be instantiated directly.
Inheritance: Abstract classes are designed to be extended by concrete classes. Subclasses inherit the properties and methods of the abstract class, and must implement any abstract methods.

Benefits of Abstract Classes

Code Reusability: Abstract classes enable you to create reusable templates for classes, avoiding redundant code.
Encapsulation: By defining abstract methods, you enforce specific behavior on subclasses, promoting consistent implementation.
Polymorphism: Abstract classes contribute to polymorphism by allowing objects of different subclasses to be treated as objects of the abstract class.

Example: Geometric Shapes

Let's consider a scenario where you need to model various geometric shapes (e.g., Circle, Square, Triangle).

abstract class Shape {
  // Abstract method for calculating area
  public abstract double calculateArea();

  // Concrete method for displaying shape information
  public void displayInfo() {
    System.out.println("This is a shape.");
  }
}

class Circle extends Shape {
  private double radius;

  public Circle(double radius) {
    this.radius = radius;
  }

  // Implementation of abstract method
  @override
  public double calculateArea() {
    return Math.PI * radius * radius;
  }
}

In this example:

Shape is an abstract class defining the calculateArea method as abstract.
Circle is a concrete subclass that implements calculateArea according to its specific shape.

Key Points to Remember

An abstract class cannot be instantiated directly.
Abstract classes can have both abstract and concrete methods.
Subclasses must implement all abstract methods from the parent abstract class.
Abstract classes enforce common structure and behavior among subclasses.

Abstract classes are a powerful tool in Java that promotes code reusability, encapsulation, and polymorphism. They are particularly useful when modeling complex hierarchies of classes with shared properties and behavior.

Abstract Class In Java