Abstract Factory

The abstract factory pattern provides a way to encapsulate a group of individual factories that have a common theme without specifying their concrete classes.

Frameworks that are providing dependency injection, like Spring, are solving this issue and probably, we won't needed Abstract Factory there.

Example - Animal factory

Each domain object (like Cat and Dog) are going to have it's own factory. That way, can would never have to call new Cat() or new Doc() constructors. Instead we tell the factory the inputs and the factory makes sure we get an instance.

This way, we can easily change Cat and Dog implementations without affecting user of our factories.

interface Animal {
    String getName();
}

class Cat implements Animal {

    private String name;

    public Cat(String name) {
        this.name = name;
    }

    @Override
    public String getName() {
        return name;
    }
}

class Dog implements Animal {

    private String name;

    public Dog(String name) {
        this.name = name;
    }

    @Override
    public String getName() {
        return name;
    }
}

interface AnimalAbstractFactory {
    Animal create();
}

class CatFactory implements AnimalAbstractFactory {

    private String name;

    public CatFactory(String name) {
        this.name = name;
    }

    @Override
    public Animal create() {
        Cat cat = new Cat(name);
        return cat;
    }
}

class DogFactory implements AnimalAbstractFactory {

    private String name;

    public DogFactory(String name) {
        this.name = name;
    }

    @Override
    public Animal create() {
        return new Dog(name);
    }
}

class AnimalFactory {

    public static Animal create(AnimalAbstractFactory factory) {
        Animal animal = factory.create();
        return animal;
    }
}

AnimalAbstractFactory can be implemented as interface or abstract class, it depends what is more useful for your problem.

Then we need to create an object, we create specific factory and as a user of such code, we no idea what instance is going to be created (because probably we shouldn't care).

Animal meow = AnimalFactory.create(new CatFactory("Meow"));
Animal gilbert = AnimalFactory.create(new DogFactory("Gilbert"));