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

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

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

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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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