pros and cons for implemeting a global object in Android/Java as singleton or DataClass

Question

There are many questions and answers on how to implement a global variable in Android/Java.

So it seems one can either implement a singleton or use a data class itself with static variables.

I am about to start a larger project and would like to start on the right foot.

I am just not sure which one to use.

Pro singleton/con Data Class

supposedly "cleaner" way (but I really don't know why)
ensures that there is really always just one representation
creates a new instance should the old one be "cleaned away" (whenever this may happen?)

Con singleton/pro Data Class

not recommendet by some (but did not find convincng reasons)
ensures that there is only one representation by design
very easy to access just by writing MyDataClass.x (vs accessing singleton requires getting access to it first somehow)
no need to pass it as a parameter

So in summary I tend to use DataClass but I am unsure because I read that this is supposedly not good programming style.

I like to add

the data this global object has to hold is quite big, more than 30k strings/keys. And this should not be cleaned at any stage so that when the app return it may crash because of that - as I read in other places eg Singletons vs. Application Context in Android? (the 3rd answer)
it's not a web application, I use only one classloader
it is multithread but only one thread is actually accessing this data
one may certainly also use this approach How to declare global variables in Android?, but isn't an ObjectClass just easier to use and access in this case?
And checking this http://developer.android.com/resources/faq/framework.html, esp under "Persistent Objects", implies that there is no real advantage for on or the other in those cases anyway.

Many thanks

score 3 · Accepted Answer · answered Nov 26 '11 at 07:49

3

Best way to implement singleton is to use enum.

public enum Singleton
{
    INSTANCE;

    public void someMethod()
    {
        // your code here
    }
}

For more details you can read Effective Java (2nd Edition)

answered Nov 26 '11 at 07:49

Dmytro Danylyk

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interesting syntax - how would one access this singleton in another instance object? – user387184 Nov 26 '11 at 07:55
2

Singleton singleton = Singleton.INSTANCE; singleton.someMethod(); or Singleton.INSTANCE.someMethod(); – Dmytro Danylyk Nov 26 '11 at 07:56

score 1 · Answer 2 · edited May 23 '17 at 12:32

First of all: There's not much difference between a class with public static member variables and a singleton class. A lot of developers prefer the singleton pattern because the code looks more natural and more Java. E.g. Singleton.Data looks like a constant access and Singleton.getData() looks like you're accessing some kind of static data.

Personally I use the static Application pattern: See Accessing resources without an Activity or Context reference

You can use onCreate to setup any kind of static data or even other singletons. E.g. I prefer to setup a singleton SQLite database like that and access it then via App.getDb(). You can use this pattern to access the application context or resources.

While using static data you should think about memory leeks. I would recommend to take a look at this article then.

pros and cons for implemeting a global object in Android/Java as singleton or DataClass

2 Answers2