Delving Deep into Java's final Keyword

Introduction to the final Keyword

The final keyword in Java serves as a mechanism to impose restrictions, thus preventing further modification. When applied, it can make a variable's value immutable, a method where it cannot be overridden, or a class non-inheritable. Its use is fundamental in many programming scenarios where constancy is desired.

Unraveling the final Keyword

Final Variables

A final variable's value can't be changed once it's initialized. This can be particularly useful for creating constant values.

For instance:

final double PI = 3.141592653589793;

Once PI is initialized with the value, any attempt to alter it in the code will result in a compile-time error.

Final Methods

When a method is declared as final, it cannot be overridden by subclasses. This is useful in cases where you want to prevent any alteration to the implementation of a method in derived classes.

class Parent {
    final void display() {
        System.out.println("This method cannot be overridden.");
    }
}

Final Classes

If you declare a class as final, it can't be subclassed (inherited). This can be useful when you want to ensure the security and integrity of your class's implementation.

final class ImmutableClass {
    // ... class content ...
}

Summary

The final keyword in Java offers a way to introduce immutability and restrictions at various levels — variables, methods, and classes. By understanding and leveraging the final keyword, AP CSA students can write code that is more robust, secure, and maintainable.

References

• The Final Keyword in Java by JavaTpoint
• Java Final Keyword Explained by GeeksforGeeks

AP CSA Homework Assignment

Assignment: Exploring the final Keyword in Java

Instructions

1. Create a Java class named Constants with the following final variables: SPEED_OF_LIGHT, GRAVITY, and PI. Initialize them with appropriate values.
2. Try modifying these constants in a method and observe the compile-time error.
3. Create another class with a final method named displayMessage which prints "This is a final method."
4. Attempt to create a subclass of this class and try to override the displayMessage method.
5. Document your observations and explain why the errors occurred.

After completing the tasks, ensure that your observations align with the properties of the final keyword and submit your assignment.