Function clash when implementing multiple interfaces

Question

I have a variant-style object foo that is capable of behaving as a java.util.Map and a java.util.List as well as other plain-old-data types. This object is written in C++ (modelled on the composite pattern) and I'm building a JNI so that I can use it in Java.

In Java, I'm motivated to write

public class foo implements 
        Streamable, 
        java.util.Map<String, foo>,
        java.util.List<foo>

Then I encounter trouble. For example, I need to implement 3 flavors of remove:

public foo remove(int index)   
public boolean remove(Object key)   
public foo remove(Object key)

The first two are for java.util.list, the final one for java.util.map. This, of course, is a problem since you cannot have two functions with the same name and parameters but different return types.

Is there a way round this?

Bad! One class. One responsibility. Your code needs refactoring :-/ — Amit Sharma, Jan 29 '14 at 16:08
@AmitSharma: not entirely; composite pattern is well established. See http://en.wikipedia.org/wiki/Composite_pattern — Bathsheba, Jan 29 '14 at 16:15
Will your single instance of `foo` be consumed as a Stream, Map, and List simultaneously? — William Morrison, Jan 29 '14 at 16:22

score 0 · Answer 1 · edited May 23 '17 at 12:07

0

You could use a LinkedHashMap.

Hash table and linked list implementation of the Map interface, with predictable iteration order. This implementation differs from HashMap in that it maintains a doubly-linked list running through all of its entries.

Please refer to this question as it discusses the same problem you're having.

edited May 23 '17 at 12:07

Community

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answered Jan 29 '14 at 16:09

Bruno Toffolo

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That's a nice class. But my problem is that the implementation is all in C++. – Bathsheba Jan 29 '14 at 16:14
@Bathsheba, so I would ask you to please update your post... This is not what you said there. :/ – Bruno Toffolo Jan 29 '14 at 16:16
I clearly say the object is written in C++ and I'm building a JNI around it. – Bathsheba Jan 29 '14 at 16:16

score 0 · Accepted Answer · answered Jan 29 '14 at 16:45

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An adapter would work. Have one class implement Map and Stream, and another class implement List and Stream. All operations required by these adapter's respective interfaces would draw from a common underlying foo instance.

answered Jan 29 '14 at 16:45

William Morrison

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Yes this is probably the best you can do given that my idea, on reflection, is fundamentally illogical. So +1 and accept. – Bathsheba Jan 29 '14 at 19:35
Could someone explain the -1 here? Also, @Bathsheba, I would recommend you refactor so `foo` doesn't implement these drastically different interfaces. I understand you're following a composite design pattern, but when the interface's behavior are so fundamentally different, I advise against it. Instead, try creating 3 separate adapters implementing Stream, list, and map, backed by the same data source. I'd be interested in your reasoning in implementing Map, and Stream on one object if you'd care to elaborate. – William Morrison Jan 30 '14 at 16:12
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In the end I went for coercion methods like `asList()` and `asMap()` which return concrete standard java types. They fitted quite well with other methods like `asString()` and `asDouble()` which I already had. Your answer certainly put me on the right track. – Bathsheba Jan 30 '14 at 16:19
Ah, great, I'm glad to hear it! – William Morrison Jan 30 '14 at 16:27

Function clash when implementing multiple interfaces

2 Answers2