Re: Clashing Interface methods

From:
 Alexey <inline_four@yahoo.com>
Newsgroups:
comp.lang.java.programmer
Date:
Mon, 27 Aug 2007 08:11:21 -0700
Message-ID:
<1188227481.970260.173090@22g2000hsm.googlegroups.com>
On Aug 27, 7:39 am, rossum <rossu...@coldmail.com> wrote:

On Sun, 26 Aug 2007 19:46:25 +0100, rossum <rossu...@coldmail.com>
wrote:

Is there a way to deal with interfaces which have clashing method
definitions?

I am trying to write my own queue, based on a Hashtable:

 public class HashQueue<E>
     extends Hashtable<Integer, E>
     implements Queue<E> { ... }

This combination beings in interfaces Collection, Map, Dictionary and
Queue. I am having problems with the method remove(). There are
different versions with different return values in the various
interfaces:

 Queue has: E remove()
 Collection has: boolean remove(Object o)
 Dictionary has: E remove(E elem)

The Queue version has a different signature to the other two so that
is not a problem. My problem is that the compiler is telling me that
the Dictionary remove does not match the Collection remove return
value and vice versa. It seems that the compiler is treating Object
and E as the same. How can I tell the compiler which of my
implementations of remove belongs to Collection and which to
Dictionary? I have tried Collection.remove and (Collection)remove but
neither work.

A short example:

   interface FileStuff {
       String read();
   }

   interface ConsoleStuff {
       int read();
   }

   class Stuff implements FileStuff, ConsoleStuff {
       public String read() { return "Hello World!"; }
// public String FileStuff.read() { return "Hello World!"; }
// public String (FileStuff)read() { return "Hello World!"; }
       public int read() { return 42; }
   }

Is there a way round this problem?

Thanks in advance.

rossum


There obviously being no direct way to solve the problem I ended up
using AbstractQueue with an internal HashMap:

  public class HashQueue<E>
      extends AbstractQueue<E> {

      private m_Data HashMap<Integer, E>;

  }

Thanks to everyone for your help.

rossum


Is there a reason why you want to map integer values that I can only
assume represent queue positions to the elements of the queue? If
your queue doesn't get elements removed from it midpoint, you should
be able to use a standard queue mechanism of push and pop. This
mechanism is of course already implemented in Queue implementations
(add and remove methods). If you need to dictate the order of the
queue upon addition of elements, PriorityQueue gives you that
functionality out of the box. Just wondering about your design...

Also, when declaring variables and class fields, try to use as generic
a type as possible, interfaces being preferred. From your example
above:
  private m_Data HashMap<Integer, E>;
won't compile until it's
  private HashMap<Integer, E> m_Data;
but should really be
  private Map<Integer, E> m_Data;

And if you do need to remove things from the middle of the queue, you
can still achieve that with a List object, which preserves any order
you give it.

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