Clarifying the D in SOLID...

gistfile1.md

Dependency Inversion Principle says do this:

class Foo
{
    IBar bar;

    public Foo(IBar bar) {
        this.bar = bar;
    }

    void Baz() {
        // Use bar
    }
}

Or this:

class Foo
{
    void Baz(IBar bar) {
        // Use bar
    }
}

Instead of this:

class Foo
{
    IBar bar = new Bar();

    void Baz() {
        // Use bar
    }
}