Constructor Injection: How many dependencies is too many?

I've been using manual constructor injection DI for a little bit now. One thing that I notice is that my constructors are starting to get rather long.

I have a class that depends on a bunch of little objects - anywhere between 6 and 10 sometimes. As I continue to break my application into smaller chunks, I could see this number increasing over time. Is this a common problem?

Obviously this is going to depend a great deal on the project. However, the basic question is this:

When do you start to get uncomfortable with the number of dependencies that a class has? What are some strategies that you use to reduce these dependencies?

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I would not worry about it.

Instead, I would worry about the class being too complex.

A class with many dependencies that uses them all but has no loops or if statements is fine. In some code I was working on recently there were around 14 dependencies in a class. However, there was only one path through the code and no logical way to group the dependencies into better classes.

A class with a small number of dependencies that contains many branch statements or complex loop conditions should be simplified.

answered 2011-08-10T11:42:22.917

Constructor Injection: How many dependencies is too many?

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