Java quiz 03: Static and instance variables

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It is important for every Java programmers to understand the difference between class(static) variables and instance variables. Therefore I wrote this quiz, which clarifies those differences.

Java quiz 3: The difference between static and instance variables

Level: Normal

What is written to the standard output as the result of executing the following code?

public class MyClass
  int x;
  static int y;

  MyClass(int i)
    x += i;
    y += i;
  public static void main(String[] args)
    new MyClass(2);
    MyClass mc = new MyClass(3);
    System.out.print(mc.x + "," + mc.y);
Author: Sar Maroof

Select the correct answer.

Answer explanation

  1. By creating the first object, we pass the parameter value 2 to the constructor.
    The statement x += i; increments the value of x by 2. the variable x is not initialized.
    Therefore, x = 0 + 2 = 2.
    The statement y += i; increments the value of y by 2. The initial value of y is 0, therefore y = 0 + 2 = 2.
  2. By creating the second object mc, we pass the variable 3 as parameter to the constructor.
    The statement x += i; increments the value of x by 3. The variable x is an instance variable, therefore
    its value for the object mc is equal to 3.
    The statement y += i; increments the value of y by 3. The variable y is a static (class) variable and its last
    value was 2. Therefore the value of y becomes 2 + 3 = 5 and that value is the same for all the objects of the class.The correct answer is c. 3, 5.

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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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  1. Thanks Sir U Clear My Confusion

    1. Thanks for your comment!

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