Question about Anonymous classes

[Ernesto Hilvano]

Hi JavaRanch,

Im preparing for OCPJP Exam and currently answering Enthuware,

I have a confusion about Anonymous classes,

It is said on enthuware that Anonymous classes cannot be declared static

which is a confusion for me because i can create a static anonymous class like the ff:

public class Test{

  static Object anonymousObj = new Object(){ 

     };

}

it compiles therefore i am confused about this answer on enthuware question "Anonymous classes cannot be declared static."

Enthuware explanation is
Only classes declared as members of top-level classes can be declared static. Such a member is a top-level nested class if it is declared static, otherwise it is a non-static inner class.
Package member classes, local classes(i.e. classes declared in methods) and anonymous classes cannot be declared static.

[Jeanne Boyarsky]

I wonder if this is a language thing. You can use the static modifier, but I don't think it is a static class. A static class (if it were to have a constructor) would allow you to create multiple instances. Your example feels more like a static variable than a static class.

[Paweł Baczyński]

Jeanne is right. In OP's example static refers to variable named anonymousObj, not the anonymous class.

[Henry Wong]

Jeanne Boyarsky wrote:You can use the static modifier, but I don't think it is a static class. A static class (if it were to have a constructor) would allow you to create multiple instances. Your example feels more like a static variable than a static class.

In my opinion, the closest analogy of a static modifier creating a static nested class, would be the static modifier for the method.

When an anonymous inner class is created within an instance method, it can access the variables/methods of the "this" instance, sort of like having the "this" instance being the outer class instance. On the other hand, when an anonymous inner classes is created within a static method, it doesn't have access to a "this" instance, and behaves more like a static nested class.

Henry

[Paul Anilprem]

As per JLS section 15.9.5:

An anonymous class is always an inner class; it is never static.

[Paul Anilprem]

Ernesto Hilvano wrote:Hi JavaRanch,

public class Test{

  static Object anonymousObj = new Object(){ 

     };

}

You are declaring the variable anonymousObj to be static. Not the anonymous class.

[Ankit Garg]

Static inner classes can have static members, non-static inner classes can't. To check you can try to do the same with your anonymous inner class as well:

public class Test{
  static Object anonymousObj = new Object(){ 
     static int a = 10; // doesn't compile
  };
  static class MyInner{ 
     static int a = 10; // does compile
  };
}

[Henry Wong]

Ankit Garg wrote:Static inner classes can have static members, non-static inner classes can't.

IMO, using a characteristic difference between regular inner classes and static inner (nested) classes, to prove whether anonymous inner classes are "static" or not, is very debatable. Anonymous inner classes are so different from regular inner/nested classes that I can easily make an argument that concludes differently.

For example, non-static inner classes needs an instance of an outer class to be instantiated. And in the cases of instances of anonymous inner classes that are instantiated during static initialization, or within static methods, there are no instances in context that be used as the instance of the outer class.

Paul Anilprem wrote:As per JLS section 15.9.5:

An anonymous class is always an inner class; it is never static.

Agreed. There is no defined behavior for "static" with anonymous inner classes. It is what it is -- and it is different from regular inner/nested classes.

Henry