CODEWITHSUNDEEP
javahashmapmultimap
user7110366
user7110366

Reputation:

MultiMap with Collection<String>

I am working on an XML file. In my XML file, there are somes nodes which have childs. This XML file has multiple tags. 

<Cat categorie="CAT 1" guid="e9fdsd8ff">
    <!--Electric energie management-->
    **<item Var="VAR1" guid="2795ddsd410d">
        <desc> Energie Smart Management 
        </desc>
        <App guid="240adsqsd" />
        <App guid="90dqddqsq" />**
    </item>
</Cat>

Like you can see, my node "item " has the argument VAR=var1 and has 2 childs. So I created a hashMap to put, for 1 node his childs like below

private Map<String, Collection <String >> multiMap = new HashMap <> ();

So I Have something like that actually : [Key=Var1, Value = [gui0,guid1,...]]

Now, I would like to know if you knew how to verify if a guid is contained in a collection associated with a key in order to retrieve this key.

For example, if I have this String : 240adsqsd. I want to recover Var1.

Thanks for your help

Upvotes: 1

Views: 426

Answers (4)

user7110366
user7110366

Reputation:

Thank you to everyone for your answers.

If I understand correctly, it is preferable that I look for a value not his key.

So let's admit that I choose this option.

Can I recure each value for a key.

If my key is Var1 for example, would it be better for me to recover all its values?

Upvotes: 0

Dici
Dici

Reputation: 25950

If I understand your question, you actually want to reverse your map because a map is good at accessing a value given a key not at finding a key given a value. Here's some pseudo-code to build the map:

map = new Map()
for item in items
    for app in item.apps
        map.put(app.guid, item.guid) // assuming guids are always unique

That would give you a Map<String, String> rather than Map<String, Collection<String>>. The former is good at telling you which item contains an application, the later is good at telling you which apps a given item contains. Given your reverse mapping map, you will be able to do the following:

// could just have Map<App, Item> appToItem if you build your map differently 
// and App and Item define hashCode and equals
public boolean findVar(String appId, Map<String, String> appToItem, Map<String, Item> itemsById) {
    Item item = itemsById.get(appToItem.get(appId));
    if (item == null) return null;
    return item.getVar();
}

Upvotes: 0

GameDroids
GameDroids

Reputation: 5662

It is possible. Say you have the key myKey and you want to know if the string mySearchString is contained in the collection behind that key.

multiMap.get("myKey").contains("mySearchString");

It will return true if mySearchString equals (case sensitive) any object in the colelction.

You have to be careful though, the method contains on a collection uses the case sensitive equals method and will only work when they are 100% equal. So when your collection contains something like "MYSEARCHstring", it won't work, as well as "The sentence that contains mySearchString".

EDIT:
(Thanks Nikolas and Dici)
Here a more complete example how to achieve that. 

String mySearchString = "mySearchString";
Map<String, Collection<String>> multiMap = new HashMap<>();
for (String key : multiMap.keySet()) {
    if (multiMap.get(key) != null && multiMap.get(key).contains(mySearchString)) {
        return key;
    }
}

If you don't know the key, you have to iterate over your map, check if one of the collections contains the searched string and then, when you found the collection (and its key) return the key.

Upvotes: 1

Joop Eggen
Joop Eggen

Reputation: 109557

A test without map modification would be:

boolean contained = multiMap.getOrDefault(key, Collections.emptyList()).contains(key);

Then there are Map.computeIfAbsent, computeIfPresent, merge if you want to update the map.

Upvotes: 0

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