Static Inner Classes Bytecode Java

Asked Dec 04 '19 at 10:12

Active Dec 04 '19 at 13:58

Viewed 248 times

I have a test class:

public class Test {

    private static class Nested1 {
        Nested2 n2 = new Nested2();
    }

    private static class Nested2 {
        Nested1 n1 = new Nested1();
    }

}

As I understand, static nested classes are regular static member of the enclosing class, that are still top-level classes. When I compile the above code, I get four files:

Test$1.class
Test$Nested1.class
Test$Nested2.class
Test.class

Compiled from "Test.java"

class Test$Nested1 {
  Test$Nested2 n2;
  private Test$Nested1();
  Test$Nested1(Test$1);
}

My questions:

Why do I have an additional class Test$1.class.
```
class Test$1 {
}
```
Why does Test$Nested1.class' constructor have an input of type: Test$1?

Test.java

public class Test {  

    private static class Nested1 {
        Nested2 n2 = new Nested2();
    }

    private static class Nested2 {
        Nested1 n1 = new Nested1();
    }

}

I am using Java 1.8.

edited Dec 04 '19 at 10:49

asked Dec 04 '19 at 10:12

Prashant Pandey

4,332
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the de-compiled code is not a valid java class. perhaps it is meant to be `Test$Nested1(Test$1){}` – Sharon Ben Asher Dec 04 '19 at 10:24
This is the class I get from javap -p. Why do you say it's invalid? – Prashant Pandey Dec 04 '19 at 10:26
did you try to compile? the methods have no bodies. the class either has to be declared `abstract` or add method bodies – Sharon Ben Asher Dec 04 '19 at 10:30
@SharonBenAsher what are you talking about? there are no methods, why does he need to have methods in his classes? he pasted **compiled** `.class` file – Vault23 Dec 04 '19 at 10:34
@SharonBenAsher javap never shows the method body, just tried. – Prashant Pandey Dec 04 '19 at 10:35
Not reproducable. I do not get `Test$1.class`! – Seelenvirtuose Dec 04 '19 at 10:42
@Seelenvirtuose I do. At least with Java 8. – Federico klez Culloca Dec 04 '19 at 10:43
Using javac, I get the four files. – Prashant Pandey Dec 04 '19 at 10:43
Which Java version are you using? – Mark Rotteveel Dec 04 '19 at 10:43
Java 1.8.0_172. – Prashant Pandey Dec 04 '19 at 10:44
1

Ah! With Java 8 I also get this class. Important information that must be included in the question! – Seelenvirtuose Dec 04 '19 at 10:46
Just curious, is it a real case or accidental findings? – Ori Marko Dec 04 '19 at 10:55
Was just brushing up on my inner classes knowledge. Created a fast example, stumbled upon this. – Prashant Pandey Dec 04 '19 at 10:55
the additional `Test$1.class` is probably a synthetic class. see proposed duplicate for details – Sharon Ben Asher Dec 04 '19 at 11:40
@SharonBenAsher I think that's the answer, thanks man. – Prashant Pandey Dec 04 '19 at 11:48

Static Inner Classes Bytecode Java

0 Answers0