Why am I not able to access static inner class through an instance

Question

Let's say we have a class Test like this,

public class Test {

    public static void main(String... args) {
    }

    public static class InnerTest {
        public void test() {
        }
    }
}

I agree that, I should access static fields using the class name, like

Test.main();
Test.InnerTest obj = new Test.InnerTest();

But we can also access the static member's through instances,

Test test = new Test();

test.main(); // Compiler warning but WORKS fine.

// But I can't do any of this.
Test.InnerTest itest = test.new InnerTest(); // Illegal enclosing instance specification for type Test.InnerTest
Test.InnerTest itest = new test.InnerTest(); // test cannot be resolved to a type
Test.InnerTest itest = test.new Test.InnerTest(); // Cannot allocate the member type Test.InnerTest using its compound name when qualified by an enclosing instance. The member type name is resolved relatively to the qualifying instance type

I just want to learn why something like this is not possible? I am not able to completely understand from the errors reported.

see if [this](http://stackoverflow.com/questions/70324/java-inner-class-and-static-nested-class) helps — Deh, Aug 20 '15 at 13:17
It's a static inner class, make a call from it from Test itself, not an object — Mackiavelli, Aug 20 '15 at 13:22

score 2 · Answer 1 · answered Aug 20 '15 at 13:20

My guess: inner classes were added later, with 1.1. By the time inner classes were being designed it was apparent allowing access to static members through the instance was a mistake. It was too late to change this for existing cases but they could avoid adding it for the new functionality.

score 0 · Answer 2 · answered Aug 20 '15 at 13:16

0

Test.InnerTest itest = test.new InnerTest(); - object test does not have method new

Test.InnerTest itest = new test.InnerTest(); - everything on the right side of new operator must by a Type

Test.InnerTest itest = test.new Test.InnerTest(); - combination of both remarks

What are really trying to do? Create instances of inner classes? Are you looking for a factory method?

answered Aug 20 '15 at 13:16

Casper

216
2
7

1

If the inner class was not static, the correct way is `test.new InnerTest();` which seems to contradict your first statement. – Codebender Aug 20 '15 at 13:58
No. Even if the inner class is not static, something test.new InnerTest() will not compile. You can't instantiate from an object reference. – Casper Aug 20 '15 at 14:19
Sorry mate. You are right. The inner class can be instantiated if it is not static. – Casper Aug 21 '15 at 08:15

score 0 · Answer 3 · answered Aug 20 '15 at 13:29

IMHO The problem is you are trying to think about it as a "calling method" way and it's nothing related with this since creating a new instance with "new" keyword is a completely different process.

The syntax for the "new" keyword is defined in the Java Languaje Specification and requires a type name following it. In the case of the static inner classes this identifier has to be constructed relative to the parent class name.

https://docs.oracle.com/javase/specs/jls/se7/jls7.pdf

It is just Java Languaje is build to work this way.

Why am I not able to access static inner class through an instance

3 Answers3