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Queue and Map interface

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  Queue and Map interface Philipp Kraus <philipp.kraus@flashpixx.de> - 2014-06-13 22:52 +0200
    Re: Queue and Map interface Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-06-13 17:32 -0400
      Re: Queue and Map interface markspace <markspace@nospam.nospam> - 2014-06-13 16:52 -0700
      Re: Queue and Map interface Philipp Kraus <philipp.kraus@flashpixx.de> - 2014-06-14 07:52 +0200
        Re: Queue and Map interface Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-06-14 08:41 -0400

#28723 — Queue and Map interface

Hello,

I would like to create a class which implements a Map and a Queue with

class myMapQueue<A,B> extends myAbstractClass implements Map<A,B>, Queue<B> {}

The problem is the remove(Object) method, because the method is defined 
in the Queue and the Map
interface in the Queue with boolean remove(Object) and in the Map with 
V remove(Object), so I get
a "clash error". How can I solve this problem.

Thanks a lot

Phil

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#28724

On 6/13/2014 4:52 PM, Philipp Kraus wrote:
> Hello,
>
> I would like to create a class which implements a Map and a Queue with
>
> class myMapQueue<A,B> extends myAbstractClass implements Map<A,B>,
> Queue<B> {}
>
> The problem is the remove(Object) method, because the method is defined
> in the Queue and the Map
> interface in the Queue with boolean remove(Object) and in the Map with V
> remove(Object), so I get
> a "clash error". How can I solve this problem.

     "Favor composition over inheritance." -- Bloch

     In short, I don't believe you can do what you want -- not in the
way you want to do it.  An alternative might be to implement Map<A,B>
in an outer class, one that also contains a Queue<B> implementation as
an inner class.  The outer class would also have a getQueue() method
to return an instance of the inner class -- whether that's a new
instance created on the fly or a single instance that's created once
per outer class is up to you.

     For even more "favoritism," you could have the outer class
implement neither Map nor Queue, and delegate both those interfaces
to inner classes.

-- 
Eric Sosman
esosman@comcast-dot-net.invalid

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#28725

On 6/13/2014 2:32 PM, Eric Sosman wrote:
>      For even more "favoritism," you could have the outer class
> implement neither Map nor Queue, and delegate both those interfaces
> to inner classes.
>

Or just have two methods to call on some generic object which return a 
"view" of that object as either a Map or a Queue.

interface MyCollection {

   Map asMap();
   Queue asQueue();

}

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#28726

On 2014-06-13 21:32:20 +0000, Eric Sosman said:

> On 6/13/2014 4:52 PM, Philipp Kraus wrote:
>> Hello,
>> 
>> I would like to create a class which implements a Map and a Queue with
>> 
>> class myMapQueue<A,B> extends myAbstractClass implements Map<A,B>,
>> Queue<B> {}
>> 
>> The problem is the remove(Object) method, because the method is defined
>> in the Queue and the Map
>> interface in the Queue with boolean remove(Object) and in the Map with V
>> remove(Object), so I get
>> a "clash error". How can I solve this problem.
> 
>      "Favor composition over inheritance." -- Bloch
> 
>      In short, I don't believe you can do what you want -- not in the
> way you want to do it.  An alternative might be to implement Map<A,B>
> in an outer class, one that also contains a Queue<B> implementation as
> an inner class.  The outer class would also have a getQueue() method
> to return an instance of the inner class -- whether that's a new
> instance created on the fly or a single instance that's created once
> per outer class is up to you.
> 
>      For even more "favoritism," you could have the outer class
> implement neither Map nor Queue, and delegate both those interfaces
> to inner classes.

Thanks you both for the idea, but it is not nice to do this with 
different inner structures, because
I need on the class the interface of Map and Queue, because an object 
of myMapQueue should
use with the Java Map or Queue structure. On the idea:

class myMapQueue<K,V> {

	private myMap implements Map<K,V> {}
	private Queue implements Queue<V> {}

	public Map<K,V> getMap() {}
	public Queue<V> getQueue() {}

}

I need always the getMap or getQueue call before I can use the internal 
datastructure.

Thanks a lot for the idea, but I need first to redfine my classes for a 
better code structure

Phil

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#28729

On 6/14/2014 1:52 AM, Philipp Kraus wrote:
> On 2014-06-13 21:32:20 +0000, Eric Sosman said:
>
>> On 6/13/2014 4:52 PM, Philipp Kraus wrote:
>>> Hello,
>>>
>>> I would like to create a class which implements a Map and a Queue with
>>>
>>> class myMapQueue<A,B> extends myAbstractClass implements Map<A,B>,
>>> Queue<B> {}
>>>
>>> The problem is the remove(Object) method, because the method is defined
>>> in the Queue and the Map
>>> interface in the Queue with boolean remove(Object) and in the Map with V
>>> remove(Object), so I get
>>> a "clash error". How can I solve this problem.
>>
>>      "Favor composition over inheritance." -- Bloch
>>
>>      In short, I don't believe you can do what you want -- not in the
>> way you want to do it.  An alternative might be to implement Map<A,B>
>> in an outer class, one that also contains a Queue<B> implementation as
>> an inner class.  The outer class would also have a getQueue() method
>> to return an instance of the inner class -- whether that's a new
>> instance created on the fly or a single instance that's created once
>> per outer class is up to you.
>>
>>      For even more "favoritism," you could have the outer class
>> implement neither Map nor Queue, and delegate both those interfaces
>> to inner classes.
>
> Thanks you both for the idea, but it is not nice to do this with
> different inner structures, because
> I need on the class the interface of Map and Queue, because an object of
> myMapQueue should
> use with the Java Map or Queue structure. On the idea:
>
> class myMapQueue<K,V> {
>
>      private myMap implements Map<K,V> {}
>      private Queue implements Queue<V> {}
>
>      public Map<K,V> getMap() {}
>      public Queue<V> getQueue() {}
>
> }
>
> I need always the getMap or getQueue call before I can use the internal
> datastructure.

     You've already discovered that Map and Queue are incompatible,
hence no class can implement both of them.  That is, there can be
no single object that is simultaneously a Map and a Queue.  That
being so, you will need an intermediary of some kind to produce
whichever view -- Queue or Map -- is needed for each use.

> Thanks a lot for the idea, but I need first to redfine my classes for a
> better code structure

     Perhaps if you described the larger problem you're trying to
solve, somebody might have ideas about alternative approaches.

     (Idle anecdote: At a job interview I was once asked how to
implement something rather similar, a blend of Map and PriorityQueue.
I didn't come up with a real solution -- but I got the job anyhow.)

-- 
Eric Sosman
esosman@comcast-dot-net.invalid

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