about inner class

[mohammed usman]

Hi,
I have a few doubts about inner class. I would be happy if anyone would clear my doubts.
1. Does the inner class accessible from other class ?
2. Can an inner class be instantiated in other class ?
Thanks in advance
usman

[Marcela Blei]

1. Does the inner class accessible from other class ?
Instances of the inner class can be accesible depending on the modifier you apply to that instances.
2. Can an inner class be instantiated in other class ?
Yes, if you have instantiate the Outer class. There is only one case when you can intantiate an Inner class without the instatiation of the Outer, that case is when the Inner class is declared static.

[Anonymous]

Hope the following example Test.java clears your doubt.
- Srini
public class Test {
public static void main(String args[]) {
Outer out=new Outer();
Outer.Inner in=out.new Inner();
System.out.println(out.outerVariable);
System.out.println(in.innerVariable);
}
}
class Outer {
public int outerVariable=10;
public class Inner {
public int innerVariable=20;
}
}

[Deepak M]

Originally posted by Marcela Blei:
There is only one case when you can intantiate an Inner class without the instatiation of the Outer, that case is when the Inner class is declared static.

Inner classes are NEVER static - they are called Nested classes

[Marcela Blei]

Originally posted by Deepak M:
Inner classes are NEVER static - they are called Nested classes

What do you mean? I don�t understand, the following code compiles fine:
public class Outer {
static class Inner {
Inner() {
System.out.println("Inner como member de la clase");
}
}
}
Please explain the difference between Nested and Inner if the point is there!

[chetan nain]

the types of inner classes are:
1. static top level inner class (also may be called as top level nested class
2. non-static inner class (i think this is also called as simply nested class in a lot of text)
3. local inner class (these may be implicitly static depending upon the declaration context(like static method) they may not be declared static, however))
4. anonymous class (same condition as pt. 4)
static inner classes definitely exist. in fact, you may get a question on the test asking your opinion if a class may be declared static. the answer is yes, a class may be declared static, but only as a static inner class
regards...

[eskay kumar]

Marcela,
The code u have given is actually defining a static nested class named inner and not an "inner" class (note: inner is not a keyword in java) which is a non static nested class.
The key difference bet static nested class and an inner class is that -
The static nested class is tied only to the outer class, not an instance of the outer class.
Eg : static variables exist for the class and not for every object of the class.
But member (i.e. non static class level) variables declared for the class exist for every object- i.e. each object has its own copy of member variables.
That's why you can make an instance of the static nested class without having an instance of the outer class, just the way you can call static methods of a class without having any instances of that class.
eskay

[mohammed usman]

Thanks for one and all who have cleared my doubt.
regards
usman