11.3.2 - Factory Method Pattern
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Introduction to Factory Method Pattern
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Today we're going to explore the Factory Method Pattern. To start, who can explain what a factory pattern generally refers to?
I believe it has to do with creating objects without specifying the exact class.
Exactly! In the Factory Method Pattern, we define an interface for creating an object and let subclasses alter the type of objects that will be created. It centralizes object creation, which makes our code cleaner and more maintainable.
Can you give us a simple example of this pattern?
Sure! Imagine a `Shape` interface with a concrete class called `Circle`. The `ShapeFactory` class can decide to create a `Circle` when requested, without the client needing to know the `Circle` class specifics.
So, it promotes loose coupling, then?
Exactly! Remember, loose coupling is key to maintainability. Now, let’s summarize: the Factory Method Pattern allows subclasses to determine object creation without knowing the specifics of the created class itself.
Benefits of Factory Method Pattern
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What benefits do you think we gain by using the Factory Method Pattern?
It probably makes the system more flexible, right?
Yes, flexibility is key! It allows for easy extension of the system when new products are added. We can create subclasses without altering existing code.
And also improves encapsulation by isolating object creation?
Exactly! This reduces the dependencies between classes. Summarizing, the benefits include enhanced flexibility, easier maintenance, improved encapsulation, and adherence to the Open/Closed Principle.
Implementing Factory Method in Java
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Let's look at an implementation example. Can someone explain what the `ShapeFactory` does?
It creates shapes based on the type string it receives, like 'circle'.
Correct! Here’s a key question: why would we use an interface here instead of directly instantiating classes?
To allow for future types of shapes to be added without changing the factory itself.
Right! This keeps the factory and the client code separated. Now, let’s wrap up by highlighting that this demonstrates the essence of the Factory Method Pattern and how it fosters cleaner architectures.
Introduction & Overview
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Quick Overview
Standard
The Factory Method Pattern is a creational design pattern that provides an interface for creating an object but allows subclasses to decide which class to instantiate. It promotes loose coupling and enhances code maintainability by centralizing object creation.
Detailed
Factory Method Pattern
The Factory Method Pattern is a foundational creational design pattern in object-oriented design, particularly in Java. It defines an interface for creating an object, but it allows subclasses to alter the type of objects that will be created. This pattern promotes the principle of loose coupling by separating the process of instantiation of objects from the implementation of the class. As a result, when a new type of object is needed, the subclasses can easily implement the interface and provide the specific implementation, enhancing code extensibility and maintainability.
Key Components:
- Product Interface: Defines the interface of objects that the factory method creates.
- Concrete Products: Implement the Product interface for different types of objects that the factory can create.
- Creator Interface: Declares the factory method.
- Concrete Creators: Override the factory method to return specific instances of the product.
In Java, the Factory Method Pattern allows developers to create objects of different types while adhering to the predefined interface, thus enabling flexibility in the system's architecture.
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Definition of Factory Method Pattern
Chapter 1 of 4
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Chapter Content
Defines an interface for creating an object but lets subclasses alter the type of objects that will be created.
Detailed Explanation
The Factory Method Pattern is a design pattern that establishes a common interface for creating objects, while allowing subclasses to provide the specific implementation of the object being created. This pattern is beneficial when a class does not know the exact class of objects it needs to create, or when it wants its subclasses to determine which class to instantiate. It encapsulates the object creation process and promotes loose coupling.
Examples & Analogies
Imagine a bakery that uses a factory to produce cakes. The bakery has a general method for producing cakes (the interface), but depending on the occasion, the specific type of cake (like a chocolate cake or vanilla cake) can vary. Each type of cake has its own recipe (subclass), but they all share the same baking process (interface). This way, the bakery can easily switch between different cake types without changing the overall baking process.
Interface Definition for Shape
Chapter 2 of 4
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Chapter Content
interface Shape {
void draw();
}
Detailed Explanation
In this code snippet, we define an interface called 'Shape' that declares a method 'draw()'. This interface serves as a blueprint for any shape that needs to be created. By using an interface, we ensure that any class implementing this interface will provide its own version of the draw method, adhering to a common contract. This contributes to polymorphism, allowing the system to work with different shapes without knowing the specific class.
Examples & Analogies
Think of the Shape interface like a set of instructions for a drawing competition. Every participant (class) must follow these instructions on how to draw (implement the draw method), but each participant can choose their own style or technique, leading to unique creations while still conforming to the same guidelines.
Concrete Shape Class - Circle
Chapter 3 of 4
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Chapter Content
class Circle implements Shape {
public void draw() {
System.out.println("Drawing Circle");
}
}
Detailed Explanation
Here, we have a concrete implementation of the Shape interface named 'Circle'. The Circle class implements the 'draw()' method defined in the Shape interface, providing its specific behavior by printing 'Drawing Circle' to the console. This implementation shows how we can define a specific type of shape and its behavior while still being able to use the Shape interface elsewhere in the program.
Examples & Analogies
Consider the Circle class like a specific participant who enters the drawing competition with their unique interpretation of how to draw a circle. Just as this artist follows the competition rules but infuses their own flair into the final piece, the Circle class adheres to the Shape interface while providing its personalized draw function.
Shape Factory Class
Chapter 4 of 4
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Chapter Content
class ShapeFactory {
public Shape getShape(String type) {
if (type.equalsIgnoreCase("circle")) return new Circle();
return null;
}
}
Detailed Explanation
The ShapeFactory class plays the role of the factory in the Factory Method Pattern. It contains a method called 'getShape' that takes a string parameter 'type' to determine which shape object to create. If the type is 'circle', it returns a new instance of Circle. Otherwise, it returns null. This method abstracts the object creation process, allowing the rest of the application to request shapes without needing to know about the specific classes involved.
Examples & Analogies
Think of the ShapeFactory as the ordering desk at the bakery. When a customer requests a cake (shape), the desk (factory) checks the order details (type) and decides which cake to bake (create). If the order is for a chocolate cake, the desk instructs the kitchen to produce it, simplifying the selection process for the customer!
Key Concepts
-
Factory Method Pattern: An interface for creating objects while allowing subclasses to specify the types.
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Loose Coupling: Reducing dependencies between objects to enhance maintainability.
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Creator Interface: The interface that declares the factory method.
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Concrete Product: The specific class instance created by the factory.
Examples & Applications
In a GUI framework, the Factory Method can be used to create specific widgets like buttons, instead of instantiating them directly in the client code.
A drawing application could utilize the Factory Method to create various shapes based on user input, such as 'Circle', 'Square', etc.
Memory Aids
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Rhymes
In a code so neat and tidy, Factory's method is so mighty. For different objects, it will say, 'Subclass, make it your own way!'
Stories
Imagine a toy factory where every toy is unique. Instead of having every toy made by one person, there are many specialized workers. Each worker knows how to make a specific toy, ensuring variety and quality without changing the whole factory's work.
Memory Tools
F - Factory, M - Method, P - Pattern: Factory Method Pattern keeps classes neat & different!
Acronyms
FMP - Factory Method Pattern facilitates easy creation while keeping it flexible!
Flash Cards
Glossary
- Factory Method Pattern
A creational design pattern that defines an interface for creating objects, allowing subclasses to alter the type of objects that will be created.
- Loose Coupling
A design principle aimed at reducing the dependencies between objects, leading to code that is easier to understand and maintain.
- Creator Interface
An interface that declares the factory method that subclasses need to implement.
- Concrete Product
The specific implementation that a factory method creates.
Reference links
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