Queue and Map interface

Discussion in 'Java' started by Philipp Kraus, Jun 13, 2014.

  1. 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
     
    Philipp Kraus, Jun 13, 2014
    #1
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  2. Philipp Kraus

    Eric Sosman Guest

    "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, Jun 13, 2014
    #2
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  3. Philipp Kraus

    markspace Guest

    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();

    }
     
    markspace, Jun 14, 2014
    #3
  4. 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
     
    Philipp Kraus, Jun 14, 2014
    #4
  5. Philipp Kraus

    Eric Sosman Guest

    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.
    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, Jun 14, 2014
    #5
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