Java quiz 04: Overriding methods

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Hi guys, Here is a Java quiz. If you can solve this quiz and understand the right explanation of the answer, you are really good in Java! Of course, I mean before you read the answer explanation below :-).

Java quiz 4: Overriding methods

Level: Hard

Note: The classes Item and Book are two separate files in one package.

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

MySuper.java

public class MySuper
{
  int a = 4;

  public MySuper()
  {
    myMethod();
  }
  void myMethod()
  {
    a++;
    System.out.print("y" + a);
  }
}

MySub.java

public class MySub extends MySuper
{
  int b = 3;

  void myMethod()
  {
    System.out.print("y" + b);
  }
  public static void main(String[] args)
  {
    MySub mySub = new MySub();
  }
}
Author: Sar Maroof

Select the correct answer.


Answer explanation

  1. The constructor of the superclass invokes the method myMethod, which is overridden
    in the subclass MySub.
  2. The statement System.out.print(“y” + b); in the method myMethod of
    the subclass writes the string “y” and the value of the variable b
    to the standard output.
  3. The constructor of the superclass invokes the method myMethod, which is overridden in the subclass and the method tries to access the varaible b inside the subclass before it is initialized. Therefore the program writes y0 instead of y3
    to the standard output.

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Sar Maroof is graduated from HBO Amsterdam “higher professional education” when he already had a bachelor of science degree in Physics.
He is a SUN certified JSP as well as EJB. He has experience with Java since 2001 and worked 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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