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Re: multiple inheritance in Java

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On 03/07/13 10:46, Steven Simpson wrote:
> On 02/07/13 19:53, Lew wrote:
>> WIth Java 8 don't we get default methods? You can multiply-inherit
>> interfaces.
>
> I don't see how default methods help here.  You might define Position as
> an interface:
>
>    interface Position {
>      int getX();
>      int getY();
>      void setX(int x);
>      void setY(int y);
>    }
>
> ...but what default implementations can you give any of these methods
> without adding some state to Position?

This is an interesting question
It is possible to add state to an interface so that it is *almost* a class

The following compiles and runs on 64 bit Ubuntu Linux with

java version "1.8.0-ea"
Java(TM) SE Runtime Environment (build 1.8.0-ea-b96)
Java HotSpot(TM) 64-Bit Server VM (build 25.0-b38, mixed mode)

javac 1.8.0-ea

I haven't figured out all the mechanics or ramifications of this yet but 
it certainly looks like it is effectively possible to implement a form 
of multiple inheritance in Java. Not exactly an edifying prospect.

=============================================================

/* public instance variables for brevity */
class State{
     public Integer a = 0;
     public Integer b = 0;
}

interface Foo{

    /* explicitly static and final */
    Integer i = 0;
    State state = new State(); /* final reference, mutable instance */

    default public void doFoo(Integer x){
        //i = 10; /* illegal */
        Integer y = x + i;
        state.a = y + y;
        System.out.println("doingFoo, i + x is " + y);
        System.out.println("doingFoo, accessing state state.a is " + 
state.a);
    }
}

interface Bar{

    Integer i = 0;
    State state = new State();

    default public void doBar(Integer x){
        Integer y = x + i;
        state.a = y + y;
        System.out.println("doingBar, i + x is " + y);
        System.out.println("doingBar, accessing state state.a is " + 
state.a);
    }
}

/* who owns the state? */
class FooBarImpl implements Foo, Bar{
}

public class Test{
     public static void main(String[] args){
         FooBarImpl fbi = new FooBarImpl();
         fbi.doFoo(5);
	fbi.doBar(10);
     }
}

lipska

-- 
Lipska the Kat©: Troll hunter, sandbox destroyer
and farscape dreamer of Aeryn Sun

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Re: multiple inheritance in Java Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-07-01 21:52 -0400
  Re: multiple inheritance in Java Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-07-02 00:09 -0400
    Re: multiple inheritance in Java Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-07-02 08:13 -0400
      Re: multiple inheritance in Java Arne Vajhøj <arne@vajhoej.dk> - 2013-07-04 17:33 -0400
        Re: multiple inheritance in Java Sebastian <news@seyweiler.dyndns.org> - 2013-07-05 08:04 +0200
    Re: multiple inheritance in Java Jeff Higgins <jeff@invalid.invalid> - 2013-07-02 13:17 -0400
      Re: multiple inheritance in Java Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-07-02 13:40 -0400
        Re: multiple inheritance in Java Jeff Higgins <jeff@invalid.invalid> - 2013-07-02 14:29 -0400
          Re: multiple inheritance in Java Jeff Higgins <jeff@invalid.invalid> - 2013-07-02 15:12 -0400
            Re: multiple inheritance in Java Arne Vajhøj <arne@vajhoej.dk> - 2013-07-04 17:23 -0400
              Re: multiple inheritance in Java Arne Vajhøj <arne@vajhoej.dk> - 2013-07-04 17:25 -0400
          Re: multiple inheritance in Java Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-07-02 15:44 -0400
            Re: multiple inheritance in Java Jeff Higgins <jeff@invalid.invalid> - 2013-07-02 16:28 -0400
              Re: multiple inheritance in Java Jeff Higgins <jeff@invalid.invalid> - 2013-07-02 16:44 -0400
              Re: multiple inheritance in Java Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-07-02 17:13 -0400
                Re: multiple inheritance in Java Jeff Higgins <jeff@invalid.invalid> - 2013-07-02 22:12 -0400
  Re: multiple inheritance in Java Lew <lewbloch@gmail.com> - 2013-07-02 11:53 -0700
    Re: multiple inheritance in Java Steven Simpson <ss@domain.invalid> - 2013-07-03 10:46 +0100
      Re: multiple inheritance in Java lipska the kat <"nospam at neversurrender dot co dot uk"> - 2013-07-03 13:01 +0100
        Re: multiple inheritance in Java Steven Simpson <ss@domain.invalid> - 2013-07-03 14:12 +0100
          Re: multiple inheritance in Java lipska the kat <"nospam at neversurrender dot co dot uk"> - 2013-07-03 14:49 +0100
        Re: multiple inheritance in Java Arne Vajhøj <arne@vajhoej.dk> - 2013-07-06 22:19 -0400
  Re: multiple inheritance in Java Arne Vajhøj <arne@vajhoej.dk> - 2013-07-04 17:36 -0400
    Re: multiple inheritance in Java Gene Wirchenko <genew@telus.net> - 2013-07-05 11:01 -0700

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