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

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

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

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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.
You must add a return statement in method numberOfStudent().
Class School must be defined abstract.
The method numberOfStudent() in class School must have a body.

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