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Re: Object orientation question

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On 10/28/2014 5:45 AM, Andreas Leitgeb wrote:
> Robert Klemme <shortcutter@googlemail.com> wrote:
>> On 27.10.2014 21:51, Eric Sosman wrote:
>>>       Clearly, the generated code is the same: AdditionInterface extends
>>> BaseInterface, therefore any class implementing AdditionInterface also
>>> necessarily implements BaseInterface.  If the class fails to provide a
>>> method specified by BaseInterface, the code won't compile.  So the
>>> question is purely about readability and style.
>> This is not fully correct: if you check with reflection you will see
>> that there is a difference in what Class.getInterfaces() returns.
>
> You don't even need reflection to notice a difference:
>
> interface A { ... }               |  interface A { ... }
> interface B { ... }               |  interface B extends A { ... }
> class C implements A,B { ... }    |  class C implements B { ... }
> ...                               |  ...
>     B foo = new C();               |     B foo = new C();
>     A bar = foo;  // barf!         |     A bar = foo; // ok
>
> Instead of the second assignment you could have a call to a
> method that takes an A and gets passed B-typed reference foo.

     My Java compiler (Oracle's 1.8.0_20 on 64-bit Windows 7)
doesn't "barf" as you report.  Has something changed?  Are you
using a different javac?  Here's the code; I've fleshed out
the ellipses and changed one name:

	interface A {
	   void aMethod();
	}

	interface B extends A {
	   void bMethod();
	}

	class C implements A, B {
	   public void aMethod() {
	   }

	   public void bMethod() {
	   }

	   void foo() {
	      B foo = new C();
	      A bar = foo;   // fine
	   }
	}

	class D implements B {
	   public void aMethod() {
	   }

	   public void bMethod() {
	   }

	   void foo() {
	      B foo = new D();
	      A bar = foo;   // fine, no "barf"
	   }
	}

I put all this in a file called "Andreas.java", ran javac on it,
and got four class files and no complaints.

-- 
esosman@comcast-dot-net.invalid

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Object orientation question mike <mikaelpetterson@hotmail.com> - 2014-10-27 13:26 -0700
  Re: Object orientation question Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-10-27 16:51 -0400
    Re: Object orientation question Robert Klemme <shortcutter@googlemail.com> - 2014-10-27 23:51 +0100
      Re: Object orientation question Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-10-28 09:45 +0000
        Re: Object orientation question Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-10-28 08:29 -0400
          Re: Object orientation question Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-10-28 08:33 -0400
            Re: Object orientation question Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-10-28 16:26 +0000
        Re: Object orientation question Robert Klemme <shortcutter@googlemail.com> - 2014-10-29 08:35 +0100
          Re: Object orientation question Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-10-30 00:32 +0000

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