Abstract Class in Java

Abstract Class in Java

Lesson 23: Final Keyword


The `final` keyword in Java is a versatile tool that empowers developers to enforce constraints in their codebase, ensuring stability, security, and maintainability. Let's delve deeper into the various contexts in which the `final` keyword can be applied.


Final Variables:

Final variables, once assigned, cannot be modified. They act as constants, providing a guarantee against accidental modification and promoting code clarity.



class Circle {

    final double PI = 3.14159;

    final int radius;


    Circle(int radius) {

        this.radius = radius;





In this example, `PI` is declared as a final variable, ensuring its value remains constant throughout the execution of the program.


 Final Methods:


Final methods in Java cannot be overridden by subclasses, providing a level of certainty and stability to the codebase. This is particularly useful when certain methods in a class are deemed critical and should not be altered in subclasses.



class Parent {

    final void display() {

        System.out.println("This is a final method.");





In this example, the `display()` method in the `Parent` class is marked as final, preventing any subclasses from overriding it.


 Final Classes:


Final classes cannot be subclassed, offering a level of control over class inheritance. By marking a class as final, developers can ensure that its behavior remains consistent and unchanged.



final class UtilityClass {

    // Class definition




In this example, `UtilityClass` is declared as final, indicating that it cannot be extended by any other class.


 Lesson 24: Abstraction


Abstraction is a fundamental principle in object-oriented programming that fosters simplicity, modularity, and scalability by hiding complex implementation details and exposing only essential functionalities to the user. Let's explore the significance of abstraction and its impact on software design.


Hiding Implementation Details:

Abstraction allows developers to encapsulate intricate implementation details within a class, shielding users from unnecessary complexities. This promotes code readability and comprehension, as users interact with a simplified interface.


Enhanced Readability:

By abstracting away implementation complexities, code becomes more readable and understandable. Abstraction enables developers to focus on high-level concepts and behaviors, leading to cleaner and more maintainable codebases.


Encapsulation of Complexity:

Abstraction encapsulates complex behavior behind a simple and intuitive interface, promoting modularity and scalability. By isolating implementation details, changes can be made to the underlying system without affecting external users.


 Lesson 25: Abstract Class


Abstract classes in Java serve as blueprints for other classes and cannot be instantiated on their own. They may contain a mix of abstract methods (methods without a body) and concrete methods, providing a foundation for concrete subclasses to build upon.


Cannot be Instantiated:

Abstract classes cannot be instantiated directly, as they typically represent incomplete implementations or concepts that require further specialization. Instead, they serve as templates for subclasses to extend and implement.


May Contain Abstract Methods:

Abstract classes can define abstract methods, which are declared without a body and must be implemented by concrete subclasses. This allows abstract classes to define a common interface while deferring implementation details to subclasses.


Allows Code Reusability:

Abstract classes promote code reuse by providing a common interface for related subclasses. By encapsulating common behavior and characteristics, abstract classes facilitate the creation of cohesive and modular class hierarchies.



abstract class Shape {

    abstract void draw(); // Abstract method


    void display() {

        System.out.println("Displaying shape...");





In this example, `Shape` is an abstract class with an abstract method `draw()`, which must be implemented by concrete subclasses such as `Circle` and `Rectangle`.



Abstract classes and the `final` keyword are indispensable tools in Java programming, enabling developers to build robust, flexible, and maintainable software solutions. By understanding the nuances of abstraction and finality, developers can design elegant and efficient code that is easy to understand, extend, and maintain. As you continue your journey in Java development, remember to leverage these concepts judiciously to craft solutions that stand the test of time.