Java static class import in the declaring class

Question

I have a class like:

 package com.example;

 public abstract class AbstractClass<S> {
       //stuffs
 }

Then a class that extends it, and define the generic type as its own inner class:

package com.example2;

import com.example.AbstractClass;
import com.example2.MyObject.MyObjectInnerClass;

public class MyObject extends AbstractClass<MyObjectInnerClass> {

     //other stuffs

     public static class MyObjectInnerClass {

     }
}

Why is needed the import of com.example2.MyObject.MyObjectInnerClass if it stays in the same file?

user207421 · Accepted Answer · 2015-10-05 08:49:43Z

5

import com.example.AbstractClass;
import com.example2.MyObject.MyObjectInnerClass;

public class MyObject extends AbstractClass<MyObjectInnerClass> {

It is needed because the nested (not inner) class MyObjectInnerClass only exists with an unqualifed name inside the {, which comes after the use of it in the extendsclause.

A more conventional way of writing it would be:

import com.example.AbstractClass;

public class MyObject extends AbstractClass<MyObject .MyObjectInnerClass> {

answered Oct 5, 2015 at 8:49

user207421

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1 Comment

zubergu Over a year ago

This should be the accepted answer, as it actually gives the reason why.

Deltharis · Accepted Answer · 2015-10-05 08:11:31Z

2

Let's start by saying - it's not an inner class, it's a nested class (inner class is a non-static nested class).

That import is needed for two important reasons:

It needs to know which class do you mean - You could also have MyObjectInnerClass as a class in the same package as MyObject. Importless reference to such class would point to exactly that one.
That's what nested classes are for - to group classes in a logical hierarchical structure.

Note that it is customary to, instead of import, write MyObject.MyObjectInnerClass to put emphasis on the relationship between the two.

edited Oct 5, 2015 at 8:11

answered Oct 4, 2015 at 23:14

Deltharis

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3 Comments

user207421 Over a year ago

(1) isn't correct at all: either the import or the qualification is required regardless of whether there is any ambiguity. (2) isn't a reason why the import is required.

Deltharis Over a year ago

@EJP (1) is correct - since we're talking about language specification the possibility of ambiguity is enough to make import neccessery, and that's what I wrote. As for (2)... True

user207421 Over a year ago

It is not necessary. You can write the FQN. No ambiguity there.

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