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Samil Ayoub
129 lines
2.9 KiB
Markdown
129 lines
2.9 KiB
Markdown
---
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layout: pattern
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title: Factory
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folder: factory
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permalink: /patterns/factory/
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categories: Creational
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tags:
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- Gang of Four
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---
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## Also known as
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* Simple Factory
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* Static Factory Method
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## Intent
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Providing a static method encapsulated in a class called factory, in order to hide the implementation logic and makes client code focus on usage rather then initialization new objects.
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## Explanation
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Real world example
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> Lets say we have a web application connected to SQLServer, but now we want to switch to Oracle. To do so without modifying existing source code, we need to implements Simple Factory pattern, in which a static method can be invoked to create connection to a given database.
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Wikipedia says
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> Factory is an object for creating other objects – formally a factory is a function or method that returns objects of a varying prototype or class.
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**Programmatic Example**
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We have an interface "Car" and tow implementations "Ford" and "Ferrari".
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```java
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/**
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* Car interface.
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*/
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public interface Car {
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public String getDescription();
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}
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/**
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* Ford implementation.
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*/
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public class Ford implements Car {
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static final String DESCRIPTION = "This is Ford.";
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@Override
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public String getDescription() {
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return DESCRIPTION;
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}
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}
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/**
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* Ferrari implementation.
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*/
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public class Ferrari implements Car {
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static final String DESCRIPTION = "This is Ferrari.";
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@Override
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public String getDescription() {
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return DESCRIPTION;
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}
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}
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```
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Then we have the static method "getCar" to create car objects encapsulated in the factory class "CarSimpleFactory".
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```java
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/**
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* Factory of cars.
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*/
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public class CarSimpleFactory {
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/**
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* Enumeration for different types of cars.
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*/
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static enum CarType {
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FORD, FERRARI
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}
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/**
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* Factory method takes as parameter a car type and initiate the appropriate class.
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*/
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public static Car getCar(CarType type) {
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switch (type) {
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case FORD: return new Ford();
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case FERRARI: return new Ferrari();
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default: throw new IllegalArgumentException("Model not supported.");
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}
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}
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}
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```
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Now on the client code we can create differentes types of cars(Ford or Ferrari) using the factory class.
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```java
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Car car1 = CarSimpleFactory.getCar(CarSimpleFactory.CarType.FORD);
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Car car2 = CarSimpleFactory.getCar(CarSimpleFactory.CarType.FERRARI);
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LOGGER.info(car1.getDescription());
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LOGGER.info(car2.getDescription());
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```
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Program output:
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```java
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This is Ford.
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This Ferrari.
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```
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## Applicability
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Use the Simple Factory pattern when you only care about the creation of a object, not how to create and manage it.
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## Disadvantages:
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The code becomes more complicated than it should be.
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## Related patterns
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[Factory Method](https://java-design-patterns.com/patterns/factory-method/)
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[Factory Kit](https://java-design-patterns.com/patterns/factory-kit/)
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[Abstract Factory](https://java-design-patterns.com/patterns/abstract-factory/)
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