Should member variables of global objects be made global as well?

I'm developing plugins in Eclipse which mandates the use of singleton pattern for the Plugin class in order to access the runtime plugin. The class holds references to objects such as Configuration and Resources.

In Eclipse 3.0 plug-in runtime objects are not globally managed and so are not generically accessible. Rather, each plug-in is free to declare API which exposes the plug-in runtime object (e.g., MyPlugin.getInstance()

In order for the other components of my system to access these objects, I hav开发者_如何学Ce to do the following:

MyPlugin.getInstance().getConfig().getValue(MyPlugin.CONFIGKEY_SOMEPARAMETER);

, which is overly verbose IMO.

Since MyPlugin provides global access, wouldn't it be easier for me to just provide global access to the objects it manages as well?

MyConfig.getValue(MyPlugin.CONFIGKEY_SOMEPARAMETER);

Any thoughts?

(I'm actually asking because I was reading about the whole "Global variable access and singletons are evil" debates)

Any thoughts?

Yes, for the current use-case you are examining, you could marginally simplify your example code by using statics.

But think of the potential disadvantages of using statics:

• What if in a future version of Eclipse Plugin objects are globally managed?
• What if you want to reuse your configuration classes in a related Plugin?
• What if you want to use a mock version of your configuration class for unit testing?

Also, you can make the code less verbose by refactoring; e.g.

... = MyPlugin.getInstance().getConfig().getValue(MyPlugin.CONFIGKEY_P1);
... = MyPlugin.getInstance().getConfig().getValue(MyPlugin.CONFIGKEY_P2);

becomes

MyConfig config = MyPlugin.getInstance().getConfig();
... = config.getValue(MyPlugin.CONFIGKEY_P1);
... = config.getValue(MyPlugin.CONFIGKEY_P2);

You suggest that

MyPlugin.getInstance().getConfig().getValue(MyPlugin.CONFIGKEY_SOMEPARAMETER);

is too verbose and

MyConfig.getValue(MyPlugin.CONFIGKEY_SOMEPARAMETER);

might be better. By that logic, wouldn't:

getMyConfigValue(MyPlugin.CONFIGKEY_SOMEPARAMETER):

be better yet (Maybe not shorter, but simpler)? I'm suggesting you write a local helper method.

This gives you the advantage of readability without bypassing concepts that were crafted by people who have been through the effort of fixing code that was done the easy/short/simple way.

Generally globals are pretty nasty in any situation. Singletons are also an iffy concept, but they beat the hell out of public statics in a class.

Consider how you will mock out such a class. Mocking out public statics is amazingly annoying. Mocking out singletons is hard (You have to override your getter in every method that uses it). Dependency Injection is the next level, but it can be a touch call between DI and a few simple singletons.