Merge pull request #1516 from samilAyoub/add-simple-factory

Add Simple Factory Pattern implementation

factory/README.md

+---
+layout: pattern
+title: Factory
+folder: factory
+permalink: /patterns/factory/
+categories: Creational
+tags:
+ - Gang of Four
+---
+
+## Also known as
+
+* Simple 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;
+  }
+}
+```
+
+Enumeration above represents types of cars that we support (Ford and Ferrari).
+
+```java
+public enum CarType {
+  
+  /**
+   * Enumeration for different types of cars.
+   */
+  FORD(Ford::new), 
+  FERRARI(Ferrari::new);
+  
+  private final Supplier<Car> constructor; 
+  
+  CarType(Supplier<Car> constructor) {
+    this.constructor = constructor;
+  }
+  
+  public Supplier<Car> getConstructor() {
+    return this.constructor;
+  }
+}
+```
+Then we have the static method 'getCar' to create car objects encapsulated in the factory class 'CarSimpleFactory'.
+
+```java
+/**
+ * Factory of cars.
+ */
+public class CarsFactory {
+  
+  /**
+   * Factory method takes as parameter a car type and initiate the appropriate class.
+   */
+  public static Car getCar(CarType type) {
+    return type.getConstructor().get();
+  }
+}
+```
+
+Now on the client code we can create different types of cars using the factory class.
+
+```java
+var car1 = CarsFactory.getCar(CarType.FORD);
+var car2 = CarsFactory.getCar(CarType.FERRARI);
+LOGGER.info(car1.getDescription());
+LOGGER.info(car2.getDescription());;
+```
+
+Program output:
+
+```java
+This is Ford.
+This Ferrari.
+```
+## Class Diagram
+![alt text](./etc/factory.urm.png "Factory pattern class diagram")
+
+## Applicability
+Use the Simple Factory pattern when you only care about the creation of a object, not how to create and manage it.
+
+## Pros
+* Allows keeping all objects creation in one place and avoid of spreading 'new' key value across codebase.
+* Allows to writs loosely coupled code. Some of its main advantages include better testability, easy-to-understand code, swappable components, scalability and isolated features.
+
+## Cons
+* 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/)
+
+

factory/etc/factory.urm.puml

+@startuml
+package com.iluwatar.factory {
+  class App {
+    - LOGGER : Logger {static}
+    + App()
+    + main(args : String[]) {static}
+  }
+  interface Car {
+    + getDescription() : String {abstract}
+  }
+  class CarsFactory {
+    + CarsFactory()
+    + 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 ..+ CarsFactory
+Ferrari ..|> Car 
+Ford ..|> Car 
+@enduml
\ No newline at end of file

factory/pom.xml

+<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>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.factory.App</mainClass>
+    </manifest>
+    </archive>
+   </configuration>
+   </execution>
+  </executions>
+  </plugin>
+ </plugins>
+ </build>
+</project>
\ No newline at end of file

factory/src/main/java/com/iluwatar/factory/App.java

+/*
+ * 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.factory;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Factory is an object for creating other objects, it providing Providing a static method to 
+ * create and return objects of varying classes, in order to hide the implementation logic 
+ * and makes client code focus on usage rather then objects initialization and management.
+ * 
+ * <p>In this example the CarFactory is the factory class and it provides a static method to 
+ * create different cars.
+ */
+
+public class App {
+  
+  private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
+  
+  /**
+   * Program main entry point.
+   */
+  public static void main(String[] args) {
+    var car1 = CarsFactory.getCar(CarType.FORD);
+    var car2 = CarsFactory.getCar(CarType.FERRARI);
+    LOGGER.info(car1.getDescription());
+    LOGGER.info(car2.getDescription());
+  }
+}

factory/src/main/java/com/iluwatar/factory/Car.java

+package com.iluwatar.factory;
+
+/**
+ * Car interface.
+ */
+public interface Car {
+  
+  public String getDescription();
+  
+}

factory/src/main/java/com/iluwatar/factory/CarType.java

+package com.iluwatar.factory;
+
+import java.util.function.Supplier;
+
+public enum CarType {
+  
+  /**
+   * Enumeration for different types of cars.
+   */
+  FORD(Ford::new), 
+  FERRARI(Ferrari::new);
+  
+  private final Supplier<Car> constructor; 
+  
+  CarType(Supplier<Car> constructor) {
+    this.constructor = constructor;
+  }
+  
+  public Supplier<Car> getConstructor() {
+    return this.constructor;
+  }
+}

factory/src/main/java/com/iluwatar/factory/CarsFactory.java

+package com.iluwatar.factory;
+
+/**
+ * Factory of cars.
+ */
+public class CarsFactory {
+  
+  /**
+   * Factory method takes as parameter a car type and initiate the appropriate class.
+   */
+  public static Car getCar(CarType type) {
+    return type.getConstructor().get();
+  }
+}

factory/src/main/java/com/iluwatar/factory/Ferrari.java

+package com.iluwatar.factory;
+
+/**
+ * Ferrari implementation.
+ */
+public class Ferrari implements Car {
+   
+  static final String DESCRIPTION = "This is Ferrari.";
+
+  @Override
+  public String getDescription() {
+    return DESCRIPTION;
+  }
+}

factory/src/main/java/com/iluwatar/factory/Ford.java

+package com.iluwatar.factory;
+
+/**
+ * Ford implementation.
+ */
+public class Ford implements Car {
+
+  static final String DESCRIPTION = "This is Ford.";
+
+  @Override
+  public String getDescription() {
+    return DESCRIPTION;
+  }
+}

factory/src/test/java/com/iluwatar/factory/AppTest.java

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

factory/src/test/java/com/iluwatar/factory/CarsFactoryTest.java

+package com.iluwatar.factory;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+class CarsFactoryTest {
+
+	@Test
+	void shouldReturnFerrariInstance() {
+		final var ferrari = CarsFactory.getCar(CarType.FERRARI);
+		assertTrue(ferrari instanceof Ferrari);
+	}
+
+}

pom.xml

@@ -195,6 +195,7 @@
         <module>arrange-act-assert</module>
         <module>transaction-script</module>
         <module>filterer</module>
+        <module>factory</module>
     </modules>
 
     <repositories>