Queue and Map interface

P

Philipp Kraus

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
 
E

Eric Sosman

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.
 
M

markspace

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();

}
 
P

Philipp Kraus

"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
 
E

Eric Sosman

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.)
 

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