Clean the code
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Samil Ayoub
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---
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layout: pattern
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title: Simple Factory
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folder: simple-factory
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permalink: /patterns/simple-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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* 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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@ -1,35 +0,0 @@
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@startuml
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package com.iluwatar.simplefactory {
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class App {
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- LOGGER : Logger {static}
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+ App()
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+ main(args : String[]) {static}
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}
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interface Car {
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+ getDescription() : String {abstract}
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}
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class CarSimpleFactory {
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+ CarSimpleFactory()
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+ getCar(type : CarType) : Car {static}
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}
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~enum CarType {
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+ FERRARI {static}
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+ FORD {static}
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+ valueOf(name : String) : CarType {static}
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+ values() : CarType[] {static}
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}
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class Ferrari {
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~ DESCRIPTION : String {static}
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+ Ferrari()
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+ getDescription() : String
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}
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class Ford {
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~ DESCRIPTION : String {static}
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+ Ford()
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+ getDescription() : String
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}
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}
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CarType ..+ CarSimpleFactory
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Ferrari ..|> Car
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Ford ..|> Car
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@enduml
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@ -1,41 +0,0 @@
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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">
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<modelVersion>4.0.0</modelVersion>
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<parent>
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<groupId>com.iluwatar</groupId>
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<artifactId>java-design-patterns</artifactId>
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<version>1.24.0-SNAPSHOT</version>
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</parent>
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<artifactId>simple-factory</artifactId>
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<dependencies>
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<dependency>
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<groupId>org.junit.jupiter</groupId>
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<artifactId>junit-jupiter-engine</artifactId>
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<scope>test</scope>
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</dependency>
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<dependency>
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<groupId>junit</groupId>
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<artifactId>junit</artifactId>
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</dependency>
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</dependencies>
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<build>
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<plugins>
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<!-- Maven assembly plugin is invoked with default setting which we have
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in parent pom and specifying the class having main method -->
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-assembly-plugin</artifactId>
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<executions>
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<execution>
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<configuration>
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<archive>
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<manifest>
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<mainClass>com.iluwatar.simplefactory.App</mainClass>
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</manifest>
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</archive>
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</configuration>
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</execution>
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</executions>
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</plugin>
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</plugins>
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</build>
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</project>
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/*
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* The MIT License
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* Copyright © 2014-2019 Ilkka Seppälä
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.simplefactory;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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public class App {
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private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
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/**
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* Program main entry point.
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*/
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public static void main(String[] args) {
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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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}
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package com.iluwatar.simplefactory;
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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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package com.iluwatar.simplefactory;
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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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package com.iluwatar.simplefactory;
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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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package com.iluwatar.simplefactory;
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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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@ -1,14 +0,0 @@
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package com.iluwatar.simplefactory;
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import static org.junit.jupiter.api.Assertions.*;
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import org.junit.jupiter.api.Test;
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class AppTest {
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@Test
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void shouldExecuteWithoutExceptions() {
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assertDoesNotThrow(() -> App.main(new String[]{}));
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}
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}
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@ -1,15 +0,0 @@
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package com.iluwatar.simplefactory;
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import static org.junit.jupiter.api.Assertions.*;
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import org.junit.jupiter.api.Test;
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class CarSimpleFactoryTest {
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@Test
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void shouldReturnFerrariInstance() {
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final var ferrari = CarSimpleFactory.getCar(CarSimpleFactory.CarType.FERRARI);
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assertTrue(ferrari instanceof Ferrari);
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}
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}
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