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

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

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

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

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JAVA Interfaces and Abstract Classes
What will be the output?1. public interface InfA{2. protected String getName();3. }public class Test implements InfA{ public String getName(){ return "test-name"; } public static void main (String[] args){ Test t = new Test(); System.out.println(t.getName()); }}

Compilation succeed but Runtime Exception
None of these
Compilation fails due to an error on lines 2
test-name
Compilation fails due to an error on lines 1

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