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Samil Ayoub
2020-09-03 22:41:55 +01:00
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commit 2bb252e08f
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128
simple-factory/README.md
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---
layout: pattern
title: Simple Factory
folder: simple-factory
permalink: /patterns/simple-factory/
categories: Creational
tags:
- Gang of Four
---
## Also known as
* Factory
* Static Factory Method
## Intent
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.
## Explanation
Real world example
> 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.
Wikipedia says
> 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.
**Programmatic Example**
We have an interface "Car" and tow implementations "Ford" and "Ferrari".
```java
/**
* Car interface.
*/
public interface Car {
public String getDescription();
}
/**
* Ford implementation.
*/
public class Ford implements Car {
static final String DESCRIPTION = "This is Ford.";
@Override
public String getDescription() {
return DESCRIPTION;
}
}
/**
* Ferrari implementation.
*/
public class Ferrari implements Car {
static final String DESCRIPTION = "This is Ferrari.";
@Override
public String getDescription() {
return DESCRIPTION;
}
}
```
Then we have the static method "getCar" to create car objects encapsulated in the factory class "CarSimpleFactory".
```java
/**
* Factory of cars.
*/
public class CarSimpleFactory {
/**
* Enumeration for different types of cars.
*/
static enum CarType {
FORD, FERRARI
}
/**
* Factory method takes as parameter a car type and initiate the appropriate class.
*/
public static Car getCar(CarType type) {
switch (type) {
case FORD: return new Ford();
case FERRARI: return new Ferrari();
default: throw new IllegalArgumentException("Model not supported.");
}
}
}
```
Now on the client code we can create differentes types of cars(Ford or Ferrari) using the factory class.
```java
Car car1 = CarSimpleFactory.getCar(CarSimpleFactory.CarType.FORD);
Car car2 = CarSimpleFactory.getCar(CarSimpleFactory.CarType.FERRARI);
LOGGER.info(car1.getDescription());
LOGGER.info(car2.getDescription());
```
Program output:
```java
This is Ford.
This Ferrari.
```
## Applicability
Use the Simple Factory pattern when you only care about the creation of a object, not how to create and manage it.
## Disadvantages:
The code becomes more complicated than it should be.
## Related patterns
[Factory Method](https://java-design-patterns.com/patterns/factory-method/)
[Factory Kit](https://java-design-patterns.com/patterns/factory-kit/)
[Abstract Factory](https://java-design-patterns.com/patterns/abstract-factory/)

35
simple-factory/etc/simple-factory.urm.puml
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@startuml
package com.iluwatar.simplefactory {
class App {
- LOGGER : Logger {static}
+ App()
+ main(args : String[]) {static}
}
interface Car {
+ getDescription() : String {abstract}
}
class CarSimpleFactory {
+ CarSimpleFactory()
+ getCar(type : CarType) : Car {static}
}
~enum CarType {
+ FERRARI {static}
+ FORD {static}
+ valueOf(name : String) : CarType {static}
+ values() : CarType[] {static}
}
class Ferrari {
~ DESCRIPTION : String {static}
+ Ferrari()
+ getDescription() : String
}
class Ford {
~ DESCRIPTION : String {static}
+ Ford()
+ getDescription() : String
}
}
CarType ..+ CarSimpleFactory
Ferrari ..|> Car
Ford ..|> Car
@enduml

41
simple-factory/pom.xml
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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>com.iluwatar</groupId>
<artifactId>java-design-patterns</artifactId>
<version>1.24.0-SNAPSHOT</version>
</parent>
<artifactId>simple-factory</artifactId>
<dependencies>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-engine</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
</dependency>
</dependencies>
<build>
<plugins>
<!-- Maven assembly plugin is invoked with default setting which we have
in parent pom and specifying the class having main method -->
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-assembly-plugin</artifactId>
<executions>
<execution>
<configuration>
<archive>
<manifest>
<mainClass>com.iluwatar.simplefactory.App</mainClass>
</manifest>
</archive>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>

42
simple-factory/src/main/java/com/iluwatar/simplefactory/App.java
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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.simplefactory;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class App {
private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
/**
* Program main entry point.
*/
public static void main(String[] args) {
Car car1 = CarSimpleFactory.getCar(CarSimpleFactory.CarType.FORD);
Car car2 = CarSimpleFactory.getCar(CarSimpleFactory.CarType.FERRARI);
LOGGER.info(car1.getDescription());
LOGGER.info(car2.getDescription());
}
}

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simple-factory/src/main/java/com/iluwatar/simplefactory/Car.java
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package com.iluwatar.simplefactory;
/**
* Car interface.
*/
public interface Car {
public String getDescription();
}

25
simple-factory/src/main/java/com/iluwatar/simplefactory/CarSimpleFactory.java
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package com.iluwatar.simplefactory;
/**
* Factory of cars.
*/
public class CarSimpleFactory {
/**
* Enumeration for different types of cars.
*/
static enum CarType {
FORD, FERRARI
}
/**
* Factory method takes as parameter a car type and initiate the appropriate class.
*/
public static Car getCar(CarType type) {
switch (type) {
case FORD: return new Ford();
case FERRARI: return new Ferrari();
default: throw new IllegalArgumentException("Model not supported.");
}
}
}

14
simple-factory/src/main/java/com/iluwatar/simplefactory/Ferrari.java
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package com.iluwatar.simplefactory;
/**
* Ferrari implementation.
*/
public class Ferrari implements Car {
static final String DESCRIPTION = "This is Ferrari.";
@Override
public String getDescription() {
return DESCRIPTION;
}
}

14
simple-factory/src/main/java/com/iluwatar/simplefactory/Ford.java
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package com.iluwatar.simplefactory;
/**
* Ford implementation.
*/
public class Ford implements Car {
static final String DESCRIPTION = "This is Ford.";
@Override
public String getDescription() {
return DESCRIPTION;
}
}

14
simple-factory/src/test/java/com/iluwatar/simplefactory/AppTest.java
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package com.iluwatar.simplefactory;
import static org.junit.jupiter.api.Assertions.*;
import org.junit.jupiter.api.Test;
class AppTest {
@Test
void shouldExecuteWithoutExceptions() {
assertDoesNotThrow(() -> App.main(new String[]{}));
}
}

15
simple-factory/src/test/java/com/iluwatar/simplefactory/CarSimpleFactoryTest.java
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package com.iluwatar.simplefactory;
import static org.junit.jupiter.api.Assertions.*;
import org.junit.jupiter.api.Test;
class CarSimpleFactoryTest {
@Test
void shouldReturnFerrariInstance() {
final var ferrari = CarSimpleFactory.getCar(CarSimpleFactory.CarType.FERRARI);
assertTrue(ferrari instanceof Ferrari);
}
}