Java puzzle 09: Demonstrating a for loop

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The process of loops is one of the most difficult concept for beginner programmers. To master loops you need to practice and parctice again. Therefore, I demonstrate many loops for beginners to solve. This loop is a for loop, which is often used in almost every Java program. You might need a pen and a paper if you can’t memorize the process. That is not necessary for advanced and intermediate programmers.

Java puzzle 9: Demonstrating a for loop

Level: Easy

What is the output of this program and why?

public class ForLoop
  public static void main(String[] args)
    int x = 0;
    for(int i = 0; i < 5; i++)
      x += i;
Author: Sar Maroof

Answer explanation

  1. The statement for(int i = 0; i < 5; i++) means repeat the process as long as the variable i is smaller than 5 starting with an initial value of i = 0. After each repetition the value of i is incremented by 1.
  2. According to the info of the step 1, the body of the loop is 5 times executed when i = 0, 1, 2, 3, 4 and after that the execution of the body of the loop is terminated.
  3. The initial value of the variable x is 0. So, the first time the initial value of x = x + i = 0 + 0 = 0.
  4. The second time the value of x becomes x = x + i = 0 + 1 = 1.
  5. The third time the value of x becomes x = x + i = 1 + 2 = 3.
  6. The fourth time the value of x becomes x = x + i = 3 + 3 = 6.
  7. The fifth time the value of x becomes x = x + i = 6 + 4 = 10.

The correct answer is x = 10 and the statement System.out.print(x); writes 10 to the standard output.

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.

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