You should use the factory design pattern when you have a superclass with multiple subclasses and need to create instances of these subclasses based on specific input, without the client code directly instantiating them. This pattern abstracts the object creation process.
According to the provided reference: "The factory design pattern is used when we have a superclass with multiple sub-classes and based on input, we need to return one of the sub-class. This pattern takes out the responsibility of the instantiation of a class from the client program to the factory class."
Why Use a Factory Pattern?
The core purpose of the factory pattern is to provide an interface for creating objects in a superclass, while allowing subclasses to alter the type of objects that will be created. This offers several key advantages:
- Decoupling: It decouples the client code (the part of your program that needs an object) from the concrete classes being instantiated. The client interacts with the factory, not the specific class constructor.
- Flexibility: It allows you to easily introduce new product types (subclasses) or change the implementation of existing ones without modifying the client code that uses the factory.
- Maintainability: By centralizing object creation logic in the factory, it makes the codebase easier to maintain and understand.
Common Scenarios for Using the Factory Pattern
Here are some situations where the Factory Pattern is particularly useful:
- When the exact type of object to be created is not known until runtime: Based on user input, configuration settings, or external data, your application needs to decide which specific class to instantiate.
- When you want to hide the complexity of object creation: The creation process might involve multiple steps, configurations, or dependencies. The factory can encapsulate this logic.
- When you want to provide a common interface for creating objects from a family of classes: All products created by the factory share a common superclass or interface, allowing the client to work with them uniformly.
- To promote loose coupling: As mentioned, it removes the dependency of the client on concrete classes, making the system more modular and testable.
Example Use Case: Creating Different Shapes
Imagine you have a graphics application that needs to create different shapes (Circle, Square, Triangle). All these shapes might inherit from a base Shape class. Instead of the client code having new Circle(), new Square(), etc., it could call a ShapeFactory.
Shape myShape = ShapeFactory.createShape("Circle");
myShape.draw();The ShapeFactory would handle the logic of deciding whether to return a new Circle(), new Square(), or another shape based on the input string "Circle".
Benefits Summarized
- Abstraction: Hides the creation logic.
- Extensibility: Easy to add new product types.
- Maintainability: Centralized creation code.
- Flexibility: Decoupled client code.
In essence, use the factory design pattern whenever you need a structured, flexible, and maintainable way to create objects from a family of related classes, especially when the specific type needed varies at runtime.
