Java puzzle 24: Anonymous class demonstration

<< Java Puzzles   Green = Easy,  Blue = Normal,  Red = Hard
 01   02   03   04   05   06   07   08   09   10   11   12   13   14   15   16   17   18   19   20   21   22   23   24   25   26   27   28   29   30   By title 

An anonymous class is a class, which doesn’t have a name.
It is used once to override methods of a class or an interface.
For more about anonymous classes you can click here.

Note: The class Anonymous and the interface Length are two separate files in the same package.

Java puzzle 24: Anonymous class demonstration

Level: Normal

What is the output of this program and why?

public interface Length
  int x = 8;
  void getMessage(String message);
  void getNumber(int i);

public class Anonymous
  int x = 6;
  public static void main(String[] args)
    Anonymous an = new Anonymous();
    Length length = new Length()
      public void getMessage(String str)
        System.out.print(str + x);
      public void getNumber(int i)
        System.out.print("x" + i);
Author: Sar Maroof

Answer explanation

  1. The statement length.getMessage(“y”); invokes the method getMessage. The statement System.out.print(str + x); writes the parameter str and the value of the variable x┬áto the standard output. The parameter str is y and the variable x refers to the variable x inside the interface Length. So, it writes y8 to the standard output.
  2. The method getNumber is not invoked. So, the statement┬áSystem.out.print(“x” + i); will not be executed.

The answer is: y8.

If you found this difficult, you might consider reading my book Java quizmaster for beginners. It is easy to understand, organized to learn Java in 17 days and it guides you to master Java code by solving 105 quizzes and 117 assignments. This book explains each chapter properly before starting with exercises and assignments. It is available on Amazon. See inside the book here!

Please, leave your questions, feedback and suggestions in the comments below! offers a practical method to learn and improve your Java skills. It avoids unnecessary long boring theoretical explanations, but it uses many exercises and quizzes.

Sar Maroof is graduated from HBO Amsterdam "higher professional education". He is a professional computer programming teacher, gives master classes and publishes technical articles. His experience with developing software started from 2001 and he has worked as a software developer for several big as well as small companies and later as a freelancer. He is the author of Java quizmaster and Build a Java application in 7 days.

Books by Sar Maroof


 Subscribe to Sar Maroof's RSS feeds!
 Mail this page to a friend!
 Bookmark this page!

Leave a Reply

Your email address will not be published. Required fields are marked *