accessing a ConcurrentHashMap of Objects that can be ConcurrentHashMaps

Question

I'm trying to hold data in one dynamic container for productivity's sake.

I initialize it inside a class with

private final ConcurrentHashMap<String, Object> allInOne = 
    new ConcurrentHashMap<String, Object>();

allInOne.put("total", 0.0); works without error.

allInOne.put(account, new ConcurrentHashMap<String, Object>()); works without error.

allInOne.get(account).put("total", 0.0); makes javac give:

DynamicConcurrentHashMapper.java:162: error: cannot find symbol
        allInOne.get(account).put("total", 0.0);
                              ^
symbol:   method put(String,double)
location: class Object

I've seen How do I access nested HashMaps in Java?, and I'm happy to have a solution, but is there any way to do it without casting? If not, is there a better way to template allInOne?

Special Case

I agree with all that this is bad practice for strict atomicity and recommend against it to others, but I'm trying to get a working prototype done as soon as possible.

Don't do that; it's a bad idea. And it's also extremely difficult to make it properly thread-safe. — SLaks, Dec 02 '13 at 01:11
@SLaks Thank-you! Yes, I know it's bad practice, but I'd like to have a working prototype now and clean it up later. Can you offer a suggestion? Thank you so much in advance! — , Dec 02 '13 at 01:12

score 2 · Accepted Answer · answered Dec 02 '13 at 01:14

2

you need to explicitly cast the allInOne.get(account) to ConcurrentHashMap<String, Object>()

do like this.

ConcurrentHashMap<String, Object> accountMap = (ConcurrentHashMap<String, Object>)allInOne.get(account);

answered Dec 02 '13 at 01:14

Prabhakaran Ramaswamy

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Is `accountMap` a "pointer" of sorts? Will altering `accountMap` change the data it is initialized to? – Dec 02 '13 at 01:21
@Gracchus yes In java all are references except primitive datatypes if you change the reference values it will hit back. – Prabhakaran Ramaswamy Dec 02 '13 at 01:23
Wonderful! That is an excellent workaround! Thank you so much! – Dec 02 '13 at 01:25

score 0 · Answer 2 · answered Dec 02 '13 at 01:17

0

Its a really bad idea which you are tying to do. But you can do as below.

private final ConcurrentHashMap<String, ConcurrentHashMap<String, Object>> allInOne = new ConcurrentHashMap<String, ConcurrentHashMap<String, Object>>();

In this case below line will fail.

allInOne.put("total", 0.0);

But these two lines compile

allInOne.put("", new ConcurrentHashMap<String, Object>());
allInOne.get("").put("total", 0.0);

answered Dec 02 '13 at 01:17

Jayamohan

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Thank-you! Yes, strict templating won't work in my case. Can you think of an alternative that doesn't involve templating and casting? Thank you so very much in advance! – Dec 02 '13 at 01:19
@Gracchus this is better solution than my answer. – Prabhakaran Ramaswamy Dec 02 '13 at 01:21
No I don't. Do you have any valid reasons not using Generics or Casting? – Jayamohan Dec 02 '13 at 01:22
@Jayamohan Speed of coding. I just want a working prototype for a loose proof of concept of sorts. Once I'm finished with that, I will definitely rework the code to the best practices all here recommend. – Dec 02 '13 at 01:23

accessing a ConcurrentHashMap of Objects that can be ConcurrentHashMaps

2 Answers2