Java - Final - Class

In this tutorial we will learn about final class in Java programming language.

In the previous tutorials we learned about final variables and final methods.

So, we know that if we want to create a constant then we can declare a final variable. And if we want to prevent method overriding then we can define a final method.

Now, lets talk about the final class.

The final class

If we want to prevent a class from getting inherited then we set the class as final.

Syntax

final class MyClass {
  // some code goes here...
}

Where, MyClass is the name of the class and it can't be inherited as we are using the final keyword.

Note! If a class is declared as final then all its methods implicitly gets declared as final.

We can still instantiate an object of the final class.

Example #1

In the following example we are declaring the Hello class as final.

// this class can't be inherited
// as we are using final
final class Hello {
  void greetings() {
    System.out.println("Hello World");
  }
}

// inheriting Hello class is not allowed
/**
 * class Awesome extends Hello {
 *   // some code goes here...
 * }
 */

// main class
public class Example {
  public static void main(String[] args) {
    // create an object
    Hello obj = new Hello();

    // calling method
    obj.greetings();
  }
}

Output:

$ javac Example.java 
$ java Example
Hello World

If we try to inherit the Hello class then we will get the following error.

$ javac Example.java 
Example.java:10: error: cannot inherit from final Hello
 class Awesome extends Hello {
                       ^
1 error

Example #2

In the following example we have a final class Box that can't be inherited.

We also have the GiftBox class that uses the method of the Box class.

We are passing the object of the Box class to the GiftBox class to take help of its getVolume() method.

Check the passing objects as arguments to methods tutorial for more info.

// this class is declared as final
// so it can't be inherited
final class Box {
  public double getVolume(double length, double width, double height) {
    return length * width * height;
  }
}

class GiftBox {

  // member variables
  private double length;
  private double width;
  private double height;
  
  // constructor with parameters
  GiftBox(double length, double width, double height) {
    
    // initialising the variables
    this.length = length;
    this.width = width;
    this.height = height;
  }

  // this method takes Box object as argument
  // and using the Box getVolume method
  // it prints the volume of the GiftBox
  public void printVolume(Box bObj) {
    double volume = bObj.getVolume(this.length, this.width, this.height);
    System.out.println("Volume of the GiftBox: " + volume);
  }
}

// main class
public class Example {
  public static void main(String[] args) {

    // instantiate object
    Box bObj = new Box();
    GiftBox obj = new GiftBox(5, 4, 3);

    // output
    obj.printVolume(bObj);
  }
}

Output:

$ javac Example.java 
$ java Example
Volume of the GiftBox: 60.0