Nested Classes

[Supun Lakshan Dissanayake]

I tried to create an object of D by creating an object of Outer class and using it's reference to create an object of D.
Here is the code I tried.

class Outer{  
    //  
    static class D{  
        //  
    }  
}  
  
class Demo{  
  
    public static void main(String args[]){  
    	Outer.D a = new Outer.D(); // this is OK  
          
        Outer b = new Outer(); // this is OK  
        Outer.D c = b.new D(); //compile time error  
    }  
} 

I know Outer.D a = new Outer.D(); is OK and I don't need an explanation for it.
All I want to know why we can't create an object of D when we use reference variable of Outer object

Regards!!!

[Campbell Ritchie]

Please supply fuller details. What did the compiler error say? Was it anything about this is a static context?

[harshvardhan ojha]

Hi Supun, it just looks like your inner class D is inside Outer class, but it is actually not.
Static classes are as good as an outer classes, this can only behave as class level member but not instance level member.

[Supun Lakshan Dissanayake]

Oh sorry.
My mistake.
Inner should be D
and
Outer.D c = a.new D(); //compile time error
should be
Outer.D c = b.new D(); //compile time error

now the question is appear as it should.

Campbell Ritchie wrote:What did the compiler error say? Was it anything about this is a static context?

Here is the compile time error

C:\Java\Demo.java:14: error: qualified new of static class
Outer.D c = b.new D(); //compile time error
^
1 error

[vinay chaturvedi]

A static nested class behaves as any other top-level class. A static nested class interacts with the instance members of its outer class (and other classes) just like any other top-level class.

Static nested classes are accessed using the enclosing outer class name:

"Outer.D"

For example, to create an object for the static nested class, use this syntax :

Outer.D nestedObject = new Outer.D();

For non-static nested classes you can create object as :

Outer.D nestedObject = new Outer().new D();

OR,

Outer outer = new Outer();

Outer.D nestedObject = outer.new D();