CODEWITHSUNDEEP
javaclass
Eric Wiener
Eric Wiener

Reputation: 5967

Java Class Requirements

In the following problem,

1. Which of the following is true regarding Java classes?
a) All classes must have 1 parent but may have any number of children (derived or extended) classes.
b) All classes must have 1 child (derived or extended) class but may have any number of parent classes.
c) All classes must have 1 parent class and may have a single child (derived or extended) class. d) All classes can have any number (0 or more) of parent classes and any number of children (derived or extended) classes.
e) All classes can have either 0 or 1 parent class and any number of children (derived or extended) classes.

I believed the answer would be e). I thought this because all classes can have at most 1 parent class or at least 0 (the Object class has no parent class). Furthermore, you can have any number of children (assuming integers greater than or equal to 0). The correct answer was a):

All classes must have 1 parent but may have any number of children (derived or extended) classes.

Does this mean that you can't consider the Object class to be a class?

Does the Object class have a parent?

Also, I recently asked another question on Java, also from this series of assignments (actually an optional test-review, not homework). Sorry for the two posts, but I didn't think it followed correct etiqutte to combine the questions into one post.

Upvotes: 8

Views: 1450

Answers (2)

slal
slal

Reputation: 2867

The question seems to be a bit misleading. (e) seems to be the closest to the correct. The following concepts can help in understanding the question better:

  • Object class is the superclass of all the Java classes.
  • Java does not support multiple inheritance
  • Multiple Inheritance can be achieved in Java using interfaces.
  • Interfaces are not classes
  • A class which is not final can be subclassed by any number of Java classes

Upvotes: 0

user149341
user149341

Reputation:

Technically speaking, neither A nor E is correct. The Object class is unique in having no parent; every other class must have exactly one parent. Thus, it is neither true that every class must have a parent -- Object does not -- nor is it true that all classes can have zero parents -- only Object is allowed do that.

However, if we restrict the question to user-defined classes -- leaving the special case of Object out of the picture -- answer A is correct.

Upvotes: 1

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