Private methods in interfaces likely to be supported on JVM9

[Simon Ochsenreither]

Not sure if this is news or well-known, but it seems to ship with JDK9 build 54 and later: http://mail.openjdk.java.net/pipermail/jdk9-dev/2015-March/001981.html

[Dmitry Petrashko]

Hi Simon,

Private methods interfaces are already supported by JVM.
The message that you refer to is about support in javac, not in the VM. In VM it's already supported and emitted by dotty.

cat A.scala

trait A{
  private def p = "s"
  def d = p
}

object B extends A{
  def main(args: Array[String]): Unit = {
    println(d)
  }
}

dotc A.scala
javap -c -p A

Compiled from "A.scala"
public interface A {
  public A initial$A();
    Code:
       0: aload_0
       1: areturn

  private java.lang.String p();
    Code:
       0: ldc           #13                 // String s
       2: areturn

  public java.lang.String d();
    Code:
       0: aload_0
       1: invokespecial #16                 // Method p:()Ljava/lang/String;
       4: areturn
}

javap -c -p B$

ompiled from "A.scala"
public final class B$ implements A {
  public static final B$ MODULE$;

  public static {};
    Code:
       0: new           #2                  // class B$
       3: invokespecial #14                 // Method "<init>":()V
       6: return

  public B$();
    Code:
       0: aload_0
       1: invokespecial #15                 // Method java/lang/Object."<init>":()V
       4: aload_0
       5: putstatic     #17                 // Field MODULE$:LB$;
       8: aload_0
       9: invokespecial #21                 // Method A.initial$A:()LA;
      12: pop
      13: return

  public void main(java.lang.String[]);
    Code:
       0: getstatic     #29                 // Field scala/Predef$.MODULE$:Lscala/Predef$;
       3: aload_0
       4: invokeinterface #33,  1           // InterfaceMethod A.d:()Ljava/lang/String;
       9: invokevirtual #37                 // Method scala/Predef$.println:(Ljava/lang/Object;)V
      12: return
}

 

Cheers,
Dmitry

[Simon Ochsenreither]

Wow, I wasn't aware of this!

Thanks a lot for the correction!