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Re: Abstract Class versus an Interface, when no Members in Common

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On 11/3/11 4:09 PM, KevinSimonson wrote:
> I have a method that needs to be able to return either of two very
> different types of data, in one case a class consisting of a two-
> dimensional array of<int>s accompanied by a single<byte>  value, and
> in the other case just a one-dimensional array of<int>s and that's
> all. So I created an abstract class called<SearchResult>  that has no
> members, not even any constructors, and made two classes extend
> <SearchResult>, the one class having the two-dimensional array and the
> <byte>  value, and the other having the one-dimensional array. Then I
> have my method return a value of<SearchResult>.
>
> My question is, in a situation like this where there are absolutely no
> variables or methods the two classes have in common, is it better to
> have an abstract class that both classes extend, or is it better to
> have an interface that both classes implement? Or is there any
> difference between the two approaches?
>
> Kevin Simonson

Sounds almost like you want a visitor pattern instead, or an 
intermediate object:

public class SearchResult {
    public boolean isSingleArray() { ... }
    public boolean isMultipleArray() { ... }

    // Throws IllegalStateException if !isSingleArray
    public SingleArray getSingleArray() { ... }
    // Throws IllegalStateException if !isMutipleArray
    public MultipleArray getMultipleArray() { ... }

}

Alternatively, or conjointly, you can use the visitor pattern.

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Thread

Abstract Class versus an Interface, when no Members in Common KevinSimonson <kvnsmnsn@hotmail.com> - 2011-11-03 16:09 -0700
  Re: Abstract Class versus an Interface, when no Members in Common Arne Vajhøj <arne@vajhoej.dk> - 2011-11-03 19:32 -0400
  Re: Abstract Class versus an Interface, when no Members in Common markspace <-@.> - 2011-11-03 17:37 -0700
    Re: Abstract Class versus an Interface, when no Members in Common Lew <lewbloch@gmail.com> - 2011-11-03 18:10 -0700
      Re: Abstract Class versus an Interface, when no Members in Common markspace <-@.> - 2011-11-03 18:46 -0700
  Re: Abstract Class versus an Interface, when no Members in Common Roedy Green <see_website@mindprod.com.invalid> - 2011-11-03 22:06 -0700
  Re: Abstract Class versus an Interface, when no Members in Common Ian Pilcher <arequipeno@gmail.com> - 2011-11-04 00:06 -0500
  Re: Abstract Class versus an Interface, when no Members in Common Robert Klemme <shortcutter@googlemail.com> - 2011-11-04 17:57 +0100
  Re: Abstract Class versus an Interface, when no Members in Common Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2011-11-04 13:54 -0700
    Re: Abstract Class versus an Interface, when no Members in Common Wanja Gayk <brixomatic@yahoo.com> - 2011-11-08 23:15 +0100
      Re: Abstract Class versus an Interface, when no Members in Common Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2011-11-08 20:58 -0800
  Re: Abstract Class versus an Interface, when no Members in Common Roedy Green <see_website@mindprod.com.invalid> - 2011-11-04 15:17 -0700
  Re: Abstract Class versus an Interface, when no Members in Common Wanja Gayk <brixomatic@yahoo.com> - 2011-11-08 23:13 +0100

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