When writing a paper, I usually face the problem of deciding whether a sentence is cite-able or not. Let's say I am writing about optimization of an algorithm. And I used Java to implement it. So, in the introduction, I would say something like "Java is a class based object oriented language..." This information is available in many java books and online tutorials. Does the ubiquity of the sentence make it un-citeable? Or do I cite that fact. I have read many prominent papers that simply use that sentence without quoting a source. 

Or do we only cite numerical facts that go like "Java is x times slower/faster than c++". I once read an article that says "when writing a paper, you should cite every sentence that you happen to read some where." But this is unrealistic; and we might have almost as many citations as the number of sentences in the paper. 

Is there any rule that dictates on what is quotable or not?