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digitalmars.D - How to use nested class with arsd.jni

reply fp <dev fp.com> writes:
Hello,

I have a problem using nested class with arsd.jni. Here is the 
java class :

//
// File Outer.java
//
public class Outer {
     public class Inner {
       void printHello() {
           System.out.println("inner class");
       }
     }
}

//
// D code
//
import std.stdio;
import arsd.jni;
final class Outer : JavaClass!("", Outer) {
	 Import this();
	final class Inner : JavaClass!("", Inner)
	{
            // if thoses 2 imports are removed it compiles
            // but this() and printHello() cannot be called
	    Import this();
	    Import void printHello();
	}
}
void main()
{
	auto jvm = createJvm();
	auto o = new Outer();
	Outer.Inner inner = o.Inner();
         inner.printHello();
}

The compiler ends with an error: "source\app.d(44,8): Error: 
class app.Outer.Inner is forward referenced when looking for 
__ctor". If we remove the 2  Imports inside Inner, it compiles 
but the methods are unreachable !
What is the correct way to declare/use the nested Inner class ?

Thanks.
Mar 04
parent reply Adam D. Ruppe <destructionator gmail.com> writes:
On Wednesday, 4 March 2020 at 09:35:31 UTC, fp wrote:
 What is the correct way to declare/use the nested Inner class ?
Lemme hsow you the code first: --- import std.stdio; import arsd.jni; final class Outer : JavaClass!("", Outer) { Import this(); } JavaName("Outer$Inner") // the name here has teh separator dot replaced with a $. note it is the same as the .class file if you need help figuring it out final class Inner : JavaClass!("", Inner) { Import this(Outer); // then add a constructor taking the outer class as an arg Import void printHello(); } void main() { auto jvm = createJvm(); auto o = new Outer(); // and then construct it like this Inner inner = new Inner(o); inner.printHello(); } --- Basically, direct inner classes hit a bunch of compiler bugs, so the way to make it work is to flatten it, taking the inner class out and declaring as if it was a top-level thing. Which is what the JVM does internally and that's why it works btw. If you try to add a convenience method in Outer for it, you're liable to hit a "forward reference" error, which is again a compiler bug brought on by the recursive reflection done inside jni.d (I hit more compiler bugs working on this project than I have in the last 5 years of writing D combined). As seen above, you don't need to declare them together, but if you do want to try, just be sure Inner is declared before Outer in the file. Then you can do a `final` method (not Import) that just `return new .Inner(this);` or something like that. But I think you'll probably have better luck keeping it simple and flattening like this.
Mar 04
parent fp <dev fp.com> writes:
Ah, I was almost sure  JavaName had to be used for declaring 
Inner (I have made many trials !). But what I missed was the use 
of "Outer" as an argument of this(Outer) !
And also I was not sure about where to declare Inner.

Now it works. Thanks very much for your detailed answer and your 
general advice about the use of inner class.
Mar 05