Factory Method Pattern

Factory Method design pattern is one of the 2 most frequent topics for OOD.

Factory method pattern is a creational pattern which uses factory methods to deal with the problem of creating objects without specifying the exact class of object that will be created.

This is done by creating objects via factory method, either:

1. specified in an interface/abstract class and implemente (differently)
2. implemented in a base class, and be overridden in derived classes

in Java

A normal Maze Game:

public class MazeGame {
    public MazeGame() {
        Room room1 = makeRoom();
        Room room2 = makeRoom();
        room1.connect(room2);
        this.addRoom(room1);
        this.addRoom(room2);
    }

    protected Room makeRoom() {
        return new OrdinaryRoom();
    }
}

A magic game:

public class MagicMazeGame extends MazeGame {
    @Override
    protected Room makeRoom() {
        return new MagicRoom();
    }
}