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

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

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JAVA Interfaces and Abstract Classes
interface Base{ boolean m1 (); byte m2(short s);}which two code fragments will compile?1. interface Base2 implements Base {}2. abstract class Class2 extends Base { public boolean m1(){ return true; }}3. abstract class Class2 implements Base {}4. abstract class Class2 implements Base { public boolean m1(){ return (7 > 4); }}5. abstract class Class2 implements Base { protected boolean m1(){ return (5 > 7) }}

3 and 4
2 and 3
1 and 3
1 and 2
4 and 5

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

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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?

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

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