Java

Java RSS

Which type of class is not instantiated?

Please support our Java advertiser: Programming Forums - DaniWeb Sister Site

•

Join Date: Jun 2004

Posts: 2,108

Reputation: server_crash is on a distinguished road

Solved Threads: 18

server_crash server_crash is offline

Offline

Postaholic

Which type of class is not instantiated?

Apr 25th, 2005

This is kind of a weird senario. This question was at the java state championship I was at a few weeks ago. Here was the question:

Which type of class cannot be instantiated:

abstract
static
(choices I can't remember..they were wrong)

Would both abstract and static be correct answers? I've never heard of static classes, but if there is such a thing, wouldn't it be the Dot operator that calls it, and not an instantiation?

•

Join Date: Sep 2004

Posts: 7,740

Reputation: Narue has a reputation beyond repute

Solved Threads: 739

Narue

Offline

Code Goddess

Re: Which type of class is not instantiated?

Apr 25th, 2005

>Would both abstract and static be correct answers?
No, abstract is the correct answer. static only means that a nested class doesn't designate an inner class.

I'm here to prove you wrong.

•

Join Date: Jun 2004

Posts: 2,108

Reputation: server_crash is on a distinguished road

Solved Threads: 18

server_crash server_crash is offline

Offline

Postaholic

Re: Which type of class is not instantiated?

Apr 25th, 2005

•

Originally Posted by Narue

>Would both abstract and static be correct answers?
No, abstract is the correct answer. static only means that a nested class doesn't designate an inner class.

OHHH, ok. I see, the actually main class of the static nested class would also have to be static, which isn't possible. In that case, you would be instantiating a class to get to the static..Correct?

Thanks for the reply by the way.

•

Join Date: Sep 2004

Posts: 7,740

Reputation: Narue has a reputation beyond repute

Solved Threads: 739

Narue

Offline

Code Goddess

Re: Which type of class is not instantiated?

Apr 25th, 2005

>In that case, you would be instantiating a class to get to the static
Huh? No, not at all. The following is legal:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
class Outer {
  static class Nested {}
}
 
class Test {
  Outer.Nested obj = new Outer.Nested();
}
class Outer {
  static class Nested {}
}

class Test {
  Outer.Nested obj = new Outer.Nested();
}

But this is not:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
class Outer {
  class Nested {}
}
 
class Test {
  Outer.Nested obj = new Outer.Nested();
}
class Outer {
  class Nested {}
}

class Test {
  Outer.Nested obj = new Outer.Nested();
}

The difference is that a static class is somewhat like a static data member. An instance isn't required to access it.

I'm here to prove you wrong.

•

Join Date: Jun 2004

Posts: 2,108

Reputation: server_crash is on a distinguished road

Solved Threads: 18

server_crash server_crash is offline

Offline

Postaholic

Re: Which type of class is not instantiated?

Apr 25th, 2005

Well how come you couldn't consider that an answer?

•

Join Date: Sep 2004

Posts: 7,740

Reputation: Narue has a reputation beyond repute

Solved Threads: 739

Narue

Offline

Code Goddess

Re: Which type of class is not instantiated?

Apr 25th, 2005

>Well how come you couldn't consider that an answer?
Because your explanation was so convoluted I didn't understand it, but it didn't smell right.

I'm here to prove you wrong.

•

Join Date: Jun 2004

Posts: 2,108

Reputation: server_crash is on a distinguished road

Solved Threads: 18

server_crash server_crash is offline

Offline

Postaholic

Re: Which type of class is not instantiated?

Apr 26th, 2005

I was thinking since you have to call the outer class that you couldn't count it as the answer...Is this what you were meaning?

•

Join Date: Nov 2004

Posts: 6,143

Reputation: jwenting is just really nice

Solved Threads: 213

jwenting

Offline

duckman

Re: Which type of class is not instantiated?

Apr 26th, 2005

You can create instances of a static inner class, but not of an abstract class.

When you have a static inner class the Class instance for the inner class is static, but that has nothing to do with any instances of the inner class itself.

Consider an inner class to be a data member of the outer class.
In case of non-static inner classes you'll get a Class instance for the inner class for each instance of the outer class.
When you have a static inner class you'll get a single static Class instance at Class level for the outer class, therefore accessible without an instance of the outer class itself (enabling you to do new A.B() instead of new A().new B() for example).

As people are clearly allowed to attack me but I'm not allowed to defend myself, I no longer post to this site.