IMHO it's largely a side effect of first class functions. In Java in order to pass a function you need to pass an object that has the function, or an interface

IMHO it's largely a side effect of first class functions. In Java in order to pass a function you need to pass an object that has the function, or an interface with the function, so it leads to a lot of line noise and thus people don't do it much. DI doesn't look impressive in a functional language because it's so well supported, but if you look at something like a global accumulator in a functional language you'll need a monad because you need state. eg in Java it's easier to write: int accum = 0; for(int i : collection){ accum +=i; } rather than collection.reduce(new IReduce<int> { int reduce(int accum, int i){ return i + accum; } }) I'm a bit rusty on Java so the syntax may be off but you get the idea, where as in a functional language (F#) that code is reduced to: collection |> Seq.reduce + Or in an imperative language that supports function passing (C#) collection.sum((a,b) => a+b)