Java quiz 20: Convert from a class to interfaces

  Quizzes     Assignments     Puzzles     Easy exercises     Required knowledge  
< Java Quizzes    Green = Easy,  Blue = Normal,  Red = Hard
Select    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 

In this quiz InterfaceA extends InterfaceB. The class MyClass implements InterfaceA.
The question is whether it is allowed to convert from MyClass to both interfaces
and what the consequences would be.

Java quiz 20: Convert from a class to interfaces

Level: Normal

Note: The class MyClass and the interfaces InterfaceA and InterfaceB are three separate files in one package.

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

public interface InfB
  int x = 3;
  int myMethod();

public interface InfA extends InfB
  int x = 7;

public class MyClass implements InfA
  int x = 5;
  public int myMethod()
    return x;
  public static void main(String[] args)
    InfA infA = new MyClass();
    InfB infB = new MyClass();
    MyClass mc = new MyClass();

Author: Sar Maroof

Select the correct answer.

Answer explanation

  1. By converting from a class to interfaces, the interface can acces the overridden methods.
  2. The overridden method myMethod returns the variable x of the class MyClass. Therefore the methods infB.myMethod(), infA.myMethod() and infB.myMethod()
    return 5, which is the value of the variable x of MyClass.

The correct answer is: c.

Sar Maroof is a professional software development teacher, gives master classes and publishes technical articles. He is also an expert software developer and worked for several big as well as small companies and later as a freelancer.

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

Leave a Reply