What are the practical uses of Factory Method Pattern?

Question

I\'m pretty new to Design Patterns.I just came across Factory Design Pattern. I understood that it delegates the instantiation to subclasses. But I didn\'t get the actual ap

Answer 1

Suppose you have a queue that holds objects of type task.

Now, you can subclass task for various reasons. If you are loading your tasks from some source like a database, you could use a factory to determine what task type to load.

For example:

private IEnumerable GetTasks(DataTable Table){

  Task NewTask;

  foreach(DataRow Row in Table){
    switch(tasktype){
      case tasktypes.TaskTypeA:
        NewTask = NewTaskA(...);
        break;

      case TaskTypes.TaskTypeB:
        NewTask = NewTaskB(...);
        break;
      ...
    }

    yield return NewTask;
  }
}

Later you could then call virtual methods on the tasks in your queue, like "consume" or "process", for example.

The advantage to the factory approach (in this case) is that you only have to switch on task type once (when the task is created), and let polymorphism handle most everything else.