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"); }}

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

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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.
To prevent developers from further extending the class.
When default implementations of some methods are not desirable.
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?

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

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JAVA Interfaces and Abstract Classes
Which of the following statements regarding abstract classes are true?

A subclass can override a concrete method in a superclass to declare it abstract.
An abstract class can be extended.
A subclass of a non-abstract superclass can be abstract.
An abstract class can be used as a data type.
All of these

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JAVA Interfaces and Abstract Classes
What will be the output?interface A{public void method();}class One{public void method(){System.out.println("Class One method");}}class Two extends One implements A{public void method(){System.out.println("Class Two method");}}public class Test extends Two{public static void main(String[] args){A a = new Two();a.method();}}

will print Class Two method
Compilation Error
will print Class One method
compiles fine but print nothing
None of these

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