How can I make a case insensitive keyset ConcurrentHashMap in java?

Question

I am trying to replace my use of ConcurrentHashMap with mine CaseInsensitiveConcurrentHashMap. However, I cannot instantiate my hashmap. I will provide my implementations.

The hash map class - based from SO question: https://stackoverflow.com/a/8237007/850475

import java.util.concurrent.ConcurrentHashMap;

public class CaseInsensitiveConcurrentHashMap <T> extends ConcurrentHashMap<String, T>{

    @Override
    public T put(String key, T value) {
        return super.put(key.toLowerCase(), value);
    }

    public T get(String key) {
        return super.get(key.toLowerCase());
    }
}

And my code below that does not work with the new hash map:

public class tester {
    private static ConcurrentMap<String, SomeClass> items = new CaseInsensitiveConcurrentHashMap<String, SomeClass>();  
    private static ConcurrentMap<String, CaseInsensitiveConcurrentHashMap<String, Collection<SomeClass2>>> tagMap = new CaseInsensitiveConcurrentHashMap<String, CaseInsensitiveConcurrentHashMap<String, Collection<SomeClass2>>>();
}

Both lines in tester fail. This is my error message:

Incorrect number of arguments for type CaseInsensitiveConcurrentHashMap<T>; it cannot be parameterized with arguments <String, Collection<SomeClass>>

Any idea as of what I can try?

Your map has only one type parameter, so you should pass it only one (remove the `String`s) — kiheru, Aug 19 '13 at 15:34
Be aware, that your get method is not going to get called since it is not overriding Map.get(). You should also override the other put methods in ConcurrentHashMap. — Michael Krussel, Aug 19 '13 at 15:38

score 3 · Answer 1 · answered Aug 19 '13 at 15:35

3

class CaseInsensitiveConcurrentHashMap <T>

Your hashmap takes a single generic parameter.

Therefore, when you use it, you must pass only one generic parameter.

answered Aug 19 '13 at 15:35

SLaks

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Can you give me an example of how I can initialize this new map with key value pair of `String` to `T`? – Stephen D Aug 19 '13 at 15:40
@StephenD: What don't you understand? – SLaks Aug 19 '13 at 16:18
Well, initializing a regular `ConcurrentMap`, you can initialize with `` rather than only `` – Stephen D Aug 19 '13 at 16:20

score 3 · Accepted Answer · answered Aug 19 '13 at 15:36

3

The CaseInsensitiveConcurrentHashMap has only one generalized parameter for the values, so it should be instanced using new CaseInsensitiveConcurrentHashMap<SomeClass>()

answered Aug 19 '13 at 15:36

cyberz

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Will this index the generic class by `String`? – Stephen D Aug 19 '13 at 15:41
@StephenD By extending `ConcurrentHashMap`, `CaseInsensitiveConcurrentHashMap` has already provided `String` as the type argument for keys. – Paul Bellora Aug 19 '13 at 15:43
1

Yes it should using case insensitive keys. Also note that a much better approach would be using composition over inheritance since you can't be sure that all methods will self-use the overridden put() (eg. putAll). – cyberz Aug 19 '13 at 15:43
Is there a way to allow initializing a new instance like `ConcurrentMap > cichm = new CaseInsensitiveConcurrentHashMap>();` ? – Stephen D Aug 19 '13 at 15:47
Your solution works for me. +1 if I can find a way to use it the way in my last comment question – Stephen D Aug 19 '13 at 15:52
2

It would be enough to parametrize the generic class with 2 parameters, anyway since the implementation relies on the fact that the keys are strings there's no point in doing that. – cyberz Aug 19 '13 at 15:53

How can I make a case insensitive keyset ConcurrentHashMap in java?

2 Answers2