In this post, I will help you understand more deeply about the final modifier in Java - how it affects your program. By understanding how the final modifier is used, you will have more flexibility in designing your programs.

 

1. Final Class in Java

When a class is marked as final, it cannot be subclassed. In other words, if we don’t want a class to be able to be extended by another class, mark it as final. Here’s an example:

public final class PrettyCat {
}

If we try to extend this final class like this:

class MyCat extends PrettyCat {
}

Compile error: error: cannot inherit from final PrettyCat

So the final modifier is used to prevent a class from being inherited by others. Java has many final classes: String, System, Math, Integer, Boolean, Long, etc.

 

NOTES:

- There is no final interface in Java, as the purpose of interface is to be implemented.

- We cannot have a class as both abstract and final, because the purpose of an abstract class is to be inherited.

 

2. Final Method in Java

When a method is marked as final, it cannot be overridden. Let’s look at the following example:

public class Cat {
	public final void meow() {
		System.out.println("Meow Meow!");
	}
}

Here, the meow() method is marked as final. If we attempt to override it in a subclass like this:

class BlackCat extends Cat {
	public void meow() {
		System.out.println("Gruh gruh!");
	}
}

The Java compiler will issue a compile error: error:

meow() in BlackCat cannot override meow() in Cat

So use the final keyword to modify a method in case we don’t want it to be overridden.

 

3. Final Variable in Java

When a variable is marked as final, it becomes a constant - meaning that the value it contains cannot be changed after declaration. Let’s see an example:

final float PI = 3.14f;

If we try to assign another value for this final variable later in the program like this:

PI = 3.1415f;

The compiler will complain:

error: cannot assign a value to final variable PI

For reference variable:

final Cat myCat = new Cat();

After this declaration, myCat cannot point to another object.

In Java, constants are always declared with the static and final modifiers, for example:

static final float PI = 3.1415f;

The final modifier can be also used in method’s arguments. For example:

void feed(final Cat theCat) {
}

This means code in the method cannot change the theCat variable.

That’s all for the final modifier. I hope you have learned something new today.

 

Related Tutorials:

• Java final keyword

 

Other Recommended Tutorials:

• 9 Rules about Constructors in Java
• 12 Rules and Examples About Inheritance in Java
• 12 Rules of Overriding in Java You Should Know
• 10 Java Core Best Practices Every Java Programmer Should Know
• Understand Interfaces in Java
• Understand Java Access Modifiers
• Java Variables Passing Examples - Pass-by-value or Pass-by-reference?
• Understand Encapsulation in Java