HashMap in a HashMap

Question

Updated:-

Problem Statement is-

I need to store these things-

For ID corresponding to 1, I need to Store these things

 - Key CGUID(String CGUID) and its Value, Key SGUID(String SGUID) and its Value, Key PGUID(String PGUID) and its Value, Key UID(String UID) and its Value, Key ALOC(String ALOC) and its Value

For ID corresponding to 2, I need to Store these things

- Key CGUID(String CGUID) and its Value, Key SGUID(String SGUID) and its Value, Key PGUID(String PGUID) and its Value, Key UID(String UID) and its Value, Key ALOC(String ALOC) and its Value

For ID corresponding to 3, I need to Store these things

- Key CGUID(String CGUID) and its Value, Key SGUID(String SGUID) and its Value, Key PGUID(String PGUID) and its Value, Key UID(String UID) and its Value, Key ALOC(String ALOC) and its Value

So for this problem I was thinking to make data structure like this-

public static LinkedHashMap<String, Integer> GUID_VALUES = new LinkedHashMap<String, Integer>();

public static LinkedHashMap<Integer, LinkedHashMap<String, Integer>> GUID_ID_MAPPING = new LinkedHashMap<Integer, LinkedHashMap<String, Integer>>();

Is there any better way to do than this?

Sounds like a tree that supports path-based queries, a la XPath. — Jim Garrison, May 28 '12 at 21:57
are CGUID key and value related from ID 1 and ID 2, in other words, it will be the same map or structure (this also applies on the others key/value pairs)? — Luiggi Mendoza, May 28 '12 at 22:08
By CGUID Key I mean String CGUID, I updated the question with more informaton. — AKIWEB, May 28 '12 at 22:11
Yes they are related to corresponding to ID's. As value can be different for each ID 1 and ID 2 — AKIWEB, May 28 '12 at 22:14
Then it looks like you need a map of maps like @DaveNewton and me have posted. Also, if you're going to use it in a web application, I'll suggest you to avoid `static` variables and use a cache mechanism like [ehcache](http://ehcache.org/) — Luiggi Mendoza, May 28 '12 at 22:25

score 2 · Answer 1 · answered May 28 '12 at 21:53

2

It's not entirely clear what you're ultimately trying to store.

If you just want a map of maps:

LinkedHashMap<Integer, LinkedHashMap<String, Integer>>

But what's all that "etc etc etc" at the end? Are there multiple "children" IDs per parent ID? If so then you probably want some sort of tree (which could be implemented by maps, but an abstraction over that would seem reasonable.)

answered May 28 '12 at 21:53

Dave Newton

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`LinkedHashMap>` on the left hand side – assylias May 28 '12 at 21:54
@assylias More likely on the right-hand side as a ctor, on the left-hand side you'd probably want to abstract the map implementation. – Dave Newton May 28 '12 at 21:55
Actually `Map>` on lhs, and what I said on rhs, right? ;-) – assylias May 28 '12 at 21:56
@assylias Nope, on the left I'd almost always use `Map>` unless I specifically needed to communicate it preserved insertion order. – Dave Newton May 28 '12 at 21:57
I just updated my question, Let me know if it stills confusing. – AKIWEB May 28 '12 at 22:00
@Nevzz03 You added a single line for "id=3" as far as I can tell--that's not additional information. You also edited *out* what some of the answers were for, making things *more* confusing. – Dave Newton May 28 '12 at 22:02
@Nevzz03 Not really--you added some carriage returns; also not additional information. AFAICT a map of maps is fine, though. – Dave Newton May 28 '12 at 22:28

score 1 · Accepted Answer · answered May 28 '12 at 21:55

1

In Java, you could achieve that by using:

public class Data {
    public static LinkedHashMap<String, Integer> GUID_VALUES = new LinkedHashMap<String, Integer>();
    public static LinkedHashMap<Integer, Map<String, Integer>> GUID_ID_MAPPING = new LinkedHashMap<Integer, Map<String, Integer>>();

    static {
        Integer someNumber = 0; //or another value, its for initialize the key
        GUID_ID_MAPPING.put(someNumber,GUID_VALUES);
    }
}

Still, I don't understand why you really need this. I'll suggest you to post your functional requirement and try to choose a better design to solve the problem.

answered May 28 '12 at 21:55

Luiggi Mendoza

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I use maps of maps fairly often (although usually abstracted), it's a pretty typical structure, isn't it? – Dave Newton May 28 '12 at 21:56
@DaveNewton yes, I'm just trying to check if the problem is bigger than this and it could have a better design solution :) – Luiggi Mendoza May 28 '12 at 21:59
@Luggi, I just updated my question, Let me know if it stills confusing. – AKIWEB May 28 '12 at 22:00
1

I understand :) It's hard to tell from the question what the actual requirements are :/ – Dave Newton May 28 '12 at 22:00

score 0 · Answer 3 · answered May 28 '12 at 21:49

0

You probably want a multi key map, as the one available in Apache Commons Collections:

http://commons.apache.org/collections/api-release/org/apache/commons/collections/map/MultiKeyMap.html

answered May 28 '12 at 21:49

Emmanuel Bourg

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Hmm, not sure--not clear from the question, but it looks more like a single key, with nested maps--more like a tree. – Dave Newton May 28 '12 at 21:51

HashMap in a HashMap

3 Answers3