JAVA Interfaces and Abstract Classes
Determine output of the following code.interface A { }class C { }class D extends C { }class B extends D implements A { }public class Test extends Thread{ public static void main(String[] args){ B b = new B(); if (b instanceof A) System.out.println("b is an instance of A"); if (b instanceof C) System.out.println("b is an instance of C"); }}

b is an instance of
Nothing.
b is an instance of
b is an instance of A followed by b is an instance of

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JAVA Interfaces and Abstract Classes
Given the following piece of code:public interface Guard{ void doYourJob();}abstract public class Dog implements Guard{ }which of the following statements is correct?

This code will compile without any errors.
This code will not compile, because in the declaration of class Dog we must use the keyword extends instead of implements.
This code will not compile, because class Dog must implement method doYourJob() from interface Guard.
This code will not compile, because method doYourJob() in interface Guard must be defined abstract.

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JAVA Interfaces and Abstract Classes
In Java, declaring a class abstract is useful

When it doesn't make sense to have objects of that class.
When it makes sense to have objects of that class.
When default implementations of some methods are not desirable.
To prevent developers from further extending the class.
To force developers to extend the class not to use its capabilities.

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JAVA Interfaces and Abstract Classes
Given the following piece of code:public class School{ public abstract double numberOfStudent();}which of the following statements is true?

The keywords public and abstract cannot be used together.
The method numberOfStudent() in class School must have a body.
You must add a return statement in method numberOfStudent().
Class School must be defined abstract.

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