Why `Outer.Inner inner = o.new Inner();` not `Outer.Inner inner = o.new Outer.Inner();`?

user10082400 :

class Outer {    
    class Inner {       

    }    
}

public class Demo {
    public static void main(String args[]) {

        Outer o = new Outer();
        Outer.Inner inner = o.new Inner();    

    }    
}

Why is

Outer.Inner inner = o.new Inner();

not

Outer.Inner inner = o.new Outer.Inner();

i.e. why qualifying type declaration of inner with outer class name, but not qualifying the inner class' constructor with the outer class name?

Thanks.

Andy Turner :

From the JLS 15.9, you are talking about a qualified class instance creation expression:

Qualified class instance creation expressions begin with a Primary expression or an ExpressionName

(Yours starts with a primary expression)

The syntax is given as:

ClassInstanceCreationExpression:
  UnqualifiedClassInstanceCreationExpression
  ExpressionName . UnqualifiedClassInstanceCreationExpression
  Primary . UnqualifiedClassInstanceCreationExpression

UnqualifiedClassInstanceCreationExpression:
  new [TypeArguments] ClassOrInterfaceTypeToInstantiate ( [ArgumentList] ) [ClassBody]

ClassOrInterfaceTypeToInstantiate:
  {Annotation} Identifier {. {Annotation} Identifier} [TypeArgumentsOrDiamond]

TypeArgumentsOrDiamond:
  TypeArguments 
  <>

A bit lower down, in 15.9.1, it says:

The Identifier in ClassOrInterfaceTypeToInstantiate must unambiguously denote an inner class that is accessible, non-final, not an enum type, and a member of the compile-time type of the Primary expression or the ExpressionName. Otherwise, a compile-time error occurs.

So, it has to be a member of the type of the expression. As such, there is no need to qualify it, as it cannot be anything but a class inside Outer.

It would simply be redundant to have to specify the Outer..