Static nested class

[newbiecpp]

Java can declare a static nested class. Does C++ have same thing like?

class Outer {
public:
static class Inner {
...
};

....
};

I can compile this code. But my question is what's difference between Java
and C++ in term of static nested class? In which case, it is good design to
use static nested class?

Thanks in advance.

 

[Victor Bazarov]

Java can declare a static nested class. Does C++ have same thing like?

class Outer {
public:
static class Inner {
...
};

...
};

I can compile this code. But my question is what's difference between Java
and C++ in term of static nested class? In which case, it is good design to
use static nested class?

In Java, when you create a nested class, its instance is automatically
created and added to the object or to the class (if the nested class is
declared static), at least that's how I remember it. In C++ when you
declare a nested class, you only define a type, there is no instance
involved. In order to declare/define an instance, you need to explicitly
do that:

class Outer {
public:
class Inner {
...
};

Inner non_static_member;
static Inner static_member;
};

Hence, there is no need to declare the type 'static', you do that when
you declare the actual data member.

So, the answer could be "no, C++ can't do that, there are no static
types only static objects", or, if you prefer, "yes, C++ can do that,
you just have to declare a static data member of the type Inner in the
'Outer'". Pick whichever answer you like better.

Victor

 

[È«±æµ¿]

In java, the static inner class has different meaning..

Every java class members (include inner classes) must be accessed by object,
not class.

Only static members can be accessed by class.

so, if you want access inner class without creation of object, you must
declare as "static inner class".

for example ..

public class Outer {
public class Inner {
};
public static class StaticInner {
};
public static void main(String[] args) {
Outer.Inner x = new Outer.Inner <-- invalid
Outer.StaticInner x = new Outer.StaticInner <-- valid
}
};