Question

I have three major classes, lets say A, B and C.
A instantiates both B and C. B also depends on C. B accesses C’s object through setter/getter methods. This is fine.
My problem is that A’s implementation is tightly coupled with B’s and C’s implementation.
I want to decouple this.
I don’t want to use the spring framework. Is there any other way? I thought of creating factories for their(B,C) initialization s but that means whenever A or C will need to access B they have to create a new instance of the Factory again.. this doesn’t seem right.
How should I solve this?
I am not sure if the IOC container is useful here?

Answer 1

A should not directly instantiate B or C. It should instead accept instances of them as constructor parameters:

public class A
{
    private B b;
    private C c;

    public A(B b, C c)
    {
        this.b = b;
        this.c = c;
    }
}

// When creating your object graph, in the "composition root":
B b = new B();
C c = new C(b);
A a = new A(b, c);

This decouples A from the details of instantiating Bs and Cs, by injecting it with those dependencies (thus, dependency injection).

To decouple A from the implementation, you’ll want to create interfaces for the functionality of B and C that A cares about. Say, Bable and Cable. Then A can accept as its constructor parameters a Bable and a Cable, and doesn’t care what class happens to implement those interfaces, or how the implementation works—just that it conforms to the contracts laid out by Bable and Cable.

Here is a fully fleshed-out example of what I am talking about: https://gist.github.com/2402514