Design Patterns: Abstract Factory vs Factory C#

The main difference between a “factory method” and an “abstract factory” is that the factory method is a method, and an abstract factory is an object.

The Factory Method:

The factory method is just a method, it can be overridden in a subclass. In other words, the Factory Method pattern uses inheritance and relies on a subclass to handle the desired object instantiation.

An object is calling its own factory method here. Therefore the only thing that could change the return value would be a subclass.

Factory Code Example:

class A {
    public void doSomething() {
        Foo f = makeFoo();
        f.whatever();   
    }

    protected Foo makeFoo() {
        return new RegularFoo();
    }
}

class B : A {
    protected Foo makeFoo() {
        //subclass is overriding the factory method 
        //to return something different
        return new SpecialFoo();
    }
}

The Abstract Factory Method:

Abstract factory is an object that has multiple factory methods on it. In other words, the Abstract Factory pattern, a class delegates the responsibility of object instantiation to another object via composition.

There is an object A, who wants to make a Foo object. Instead of making the Foo object itself (e.g., with a factory method), it’s going to get a different object (the abstract factory) to create the Foo object.

Abstract Factory Code Example:

class A {
    private Factory factory;

    public A(Factory factory) {
        this.factory = factory;
    }

    public void doSomething() {
        //The concrete class of "f" depends on the concrete class
        //of the factory passed into the constructor. If you provide a
        //different factory, you get a different Foo object.
        Foo f = factory.makeFoo();
        f.whatever();
    }
}

interface Factory {
    Foo makeFoo();
    Bar makeBar();
    Abc makeAmbiguousYetCommonlyUsedFakeClassName();
}

//need to make concrete factories that implement the "Factory" interface here

Conclusion

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Happy Coding!