Mastering Java’s Final Keyword: A Comprehensive Guide to Methods and Classes

1. Introduction …………………………………………………… Page 2
2. Understanding the Final Keyword …………………………… Page 3
2.1 What Is the Final Keyword?
2.2 Final Methods vs. Final Classes
3. Code Walkthrough and Explanation …………………………… Page 5
3.1 Parent Class Example
3.2 Child Class Example and Overriding Issues
3.3 Main Application Execution
4. Diagram: Class Inheritance and Method Finality …………… Page 8
5. Conclusion ………………………………………………… Page 10

1. Introduction

In this eBook, we embark on a journey to demystify one of Java’s important keywords—the final keyword. Whether you are a beginner or a developer with a basic understanding of object-oriented programming, this guide will illustrate how the final keyword restricts method overriding and class inheritance. We will discuss the pros and cons of using final, analyze a Java project example, and provide clear, step-by-step code walkthroughs.

To help you quickly navigate and compare different aspects of using the final keyword, we include a comparison table summarizing key details and a diagram that visualizes class relationships. This eBook is designed to be clear, concise, and optimized for SEO.

2. Understanding the Final Keyword

2.1 What Is the Final Keyword?

The final keyword in Java is used to denote that a variable, method, or class cannot be modified further. When applied to methods, it prevents overriding in subclasses. When applied to classes, it prevents inheritance altogether.

2.2 Final Methods vs. Final Classes

Below is a comparison table to highlight the differences:

Aspect	Final Method	Final Class
Purpose	Prevents method overriding	Prevents class inheritance
When to Use	When a specific behavior should not be modified	When the entire class’s behavior should remain unchanged
Inheritance Impact	Subclasses can’t change behavior for final methods	No subclass of a final class is permitted
Example	public final void display() {…}	public final class Utility {…}

● When to use final methods:
• When you want to ensure that the logic implemented in a method remains constant.
● When to use final classes:
• When you want to secure the complete implementation of a class against modification.

3. Code Walkthrough and Explanation

We analyze the below example code snippets extracted from the project files. This project demonstrates the importance of the final keyword in both methods and classes through a Parent–Child relationship.

3.1 Parent Class Example (Parent.java)

/* Parent.java */
public class Parent {
    // final method 'india' which cannot be overridden in any subclass
    public final void india() {
        System.out.println("India is great");
    }
    
    // final method 'usa' which cannot be overridden in any subclass
    public final void usa() {
        System.out.println("USA is fantastic");
    }
}

/* Parent.java */

public class Parent {

// final method 'india' which cannot be overridden in any subclass

public final void india() {

System.out.println("India is great");

}

// final method 'usa' which cannot be overridden in any subclass

public final void usa() {

System.out.println("USA is fantastic");

}

Explanation:
• The Parent class contains two methods, india() and usa(), both marked as final.
• Marking these methods as final in the Parent class enforces that any subclass cannot modify their implementations.

3.2 Child Class Example (Child.java)

/* Child.java */
public class Child extends Parent {
    // Attempting to override a final method will lead to compilation error
    // The following commented-out code is an example:
    
    // @Override
    // public void india() {
    //     // Even if the message differs, this override is disallowed due to the final modifier in Parent.
    //     System.out.println("India is great and Indians are nice");
    // }
    
    /* Proper usage: no overriding of final methods from the Parent class */
}

/* Child.java */

public class Child extends Parent {

// Attempting to override a final method will lead to compilation error

// The following commented-out code is an example:

// @Override

// public void india() {

// // Even if the message differs, this override is disallowed due to the final modifier in Parent.

// System.out.println("India is great and Indians are nice");

// }

/* Proper usage: no overriding of final methods from the Parent class */

}

Explanation:
• The class Child extends Parent.
• An attempt to override the final method india() would cause a compile-time error: “Cannot override the final method from Parent.”
• This highlights Java’s design to protect method integrity.

3.3 Main Application Execution (Main.java)

/* Main.java */
public class Main {
    public static void main(String[] args) {
        // Instantiating the Child object which inherits final methods from Parent
        Child child = new Child();
        
        // Calling the final methods from Parent via the Child instance
        child.india();  // Output: India is great
        child.usa();    // Output: USA is fantastic
    }
}

/* Main.java */

public class Main {

public static void main(String[] args) {

// Instantiating the Child object which inherits final methods from Parent

Child child = new Child();

// Calling the final methods from Parent via the Child instance

child.india(); // Output: India is great

child.usa(); // Output: USA is fantastic

}

Explanation:
• In the Main class, an object of Child is created.
• When calling child.india() and child.usa(), the final implementations from the Parent class are executed without any alterations.
• If any attempt is made to override these methods in Child, the compiler will display an error message prohibiting such changes.

Step-by-Step Explanation and Output:
1. The Parent class declares two final methods; thus, their implementation is locked.
2. The Child class, while extending Parent, does not override these methods due to the final modifier.
3. In the Main class, a Child object is created, and both methods are called.
4. The console output is as follows:
• India is great
• USA is fantastic

4. Diagram: Class Inheritance and Method Finality

Below is a conceptual diagram illustrating the relationship and restrictions enforced by the final keyword:

            [ Parent Class ]
             /         \
            /           \
  (inherits final methods)  (cannot override)
          [ Child Class ]

[ Parent Class ]

/ \

(inherits final methods) (cannot override)

[ Child Class ]

Diagram Explanation:
• The Parent Class contains final methods (india() and usa()) that are inherited by the Child Class.
• Although inheritance is allowed (Child extends Parent), overriding the final methods is prohibited, protecting the original implementation.

5. Conclusion

This article has provided an in-depth look at the Java final keyword focusing on its use with methods and classes. We learned that:

Marking methods as final prevents overriding in subclasses, ensuring method behavior remains unchanged.
Marking an entire class as final stops any further inheritance, thus securing its implementation.
A clear example was provided, including a code walkthrough that shows the step-by-step execution flow and corresponding outputs.
The comparison table and diagram enhance understanding of the concept by contrasting final methods with final classes.

By internalizing these principles, developers can design secure and predictable class hierarchies. Experiment with these examples in your own projects to see firsthand how the final modifier can protect key components in your Java applications.

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Feel free to refer back to this eBook whenever you need a refresher on restricting method and class modifications in Java!

Note: This article is AI generated.

S07L18 – Final keyword with method and classes in Java