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

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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
Nothing.
b is an instance of

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JAVA Interfaces and Abstract Classes
Which of the following class definitions defines a legal abstract class?

public class abstract A { abstract void unfinished(); }
class A { abstract void unfinished(); }
abstract class A { abstract void unfinished(); }
class A { abstract void unfinished() { } }

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