Multiple Choice Question

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Submitted by c-admin on Wed, 06/05/2019 - 02:27

QID:

506

Type:

Multiple Choice Question

Category:

Java Programmer I

Tags:

Abstraction

Question:

Which one of the following class definitions is/are a legal definition of a class that cannot be instantiated?

class Automobile{
abstract void honk(); //(1)
}
abstract class Automobile{
void honk(); //(2)
}
abstract class Automobile{
void honk(){}; //(3)
}
abstract class Automobile{
abstract void honk(){} //(4)
}
abstract class Automobile{
abstract void honk(); //(5)
}

Select 2 options

A. 1
B. 2
C. 3
D. 4
E. 5

Answer and Explanation (Click to expand)

Answer:

C - This is a valid abstract class although it doesn't have any abstract method.

E - This is a valid abstract class

Explanation:

Here are some points to remember:
A class is uninstantiable if the class is declared abstract.

If a method has been declared as abstract, it cannot provide an implementation i.e. a method body even if empty (and the class containing that method must be declared abstract).

If a method is not declared abstract, it must provide a method body (the class can be abstract but not necessarily so).

If any method in a class is declared abstract, then the whole class must be declared abstract.

Q&A Set:

Set 25

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