From 93717943707f4c12c0429cb9e04ad20ab6e2ce38 Mon Sep 17 00:00:00 2001 From: Donato Rimenti Date: Sat, 24 Feb 2018 08:21:36 +0100 Subject: [PATCH] Bael 1496 flyweight (#3598) * Added flyweight pattern example. * Refactored VehicleFactory to use computeIfAbsent method. --- .../designpatterns/flyweight/Car.java | 85 +++++++++++++++++++ .../designpatterns/flyweight/Engine.java | 31 +++++++ .../designpatterns/flyweight/Vehicle.java | 29 +++++++ .../flyweight/VehicleFactory.java | 45 ++++++++++ .../flyweight/FlyweightUnitTest.java | 42 +++++++++ 5 files changed, 232 insertions(+) create mode 100644 core-java/src/main/java/com/baeldung/designpatterns/flyweight/Car.java create mode 100644 core-java/src/main/java/com/baeldung/designpatterns/flyweight/Engine.java create mode 100644 core-java/src/main/java/com/baeldung/designpatterns/flyweight/Vehicle.java create mode 100644 core-java/src/main/java/com/baeldung/designpatterns/flyweight/VehicleFactory.java create mode 100644 core-java/src/test/java/com/baeldung/designpatterns/flyweight/FlyweightUnitTest.java diff --git a/core-java/src/main/java/com/baeldung/designpatterns/flyweight/Car.java b/core-java/src/main/java/com/baeldung/designpatterns/flyweight/Car.java new file mode 100644 index 0000000000..50f62cafaa --- /dev/null +++ b/core-java/src/main/java/com/baeldung/designpatterns/flyweight/Car.java @@ -0,0 +1,85 @@ +package com.baeldung.designpatterns.flyweight; + +import java.awt.Color; + +import javax.annotation.concurrent.Immutable; + +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +/** + * Represents a car. This class is immutable. + * + * @author Donato Rimenti + */ +@Immutable +public class Car implements Vehicle { + + /** + * Logger. + */ + private final static Logger LOG = LoggerFactory.getLogger(Car.class); + + /** + * The car's engine. + */ + private Engine engine; + + /** + * The car's color. + */ + private Color color; + + /** + * Instantiates a new Car. + * + * @param engine + * the {@link #engine} + * @param color + * the {@link #color} + */ + public Car(Engine engine, Color color) { + this.engine = engine; + this.color = color; + + // Building a new car is a very expensive operation! + try { + Thread.sleep(2000); + } catch (InterruptedException e) { + LOG.error("Error while creating a new car", e); + } + } + + /* + * (non-Javadoc) + * + * @see com.baeldung.designpatterns.flyweight.Vehicle#start() + */ + @Override + public void start() { + LOG.info("Car is starting!"); + engine.start(); + } + + /* + * (non-Javadoc) + * + * @see com.baeldung.designpatterns.flyweight.Vehicle#stop() + */ + @Override + public void stop() { + LOG.info("Car is stopping!"); + engine.stop(); + } + + /* + * (non-Javadoc) + * + * @see com.baeldung.designpatterns.flyweight.Vehicle#getColor() + */ + @Override + public Color getColor() { + return this.color; + } + +} diff --git a/core-java/src/main/java/com/baeldung/designpatterns/flyweight/Engine.java b/core-java/src/main/java/com/baeldung/designpatterns/flyweight/Engine.java new file mode 100644 index 0000000000..05d9ca98b8 --- /dev/null +++ b/core-java/src/main/java/com/baeldung/designpatterns/flyweight/Engine.java @@ -0,0 +1,31 @@ +package com.baeldung.designpatterns.flyweight; + +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +/** + * Engine for a vehicle. + * + * @author Donato Rimenti + */ +public class Engine { + + /** + * Logger. + */ + private final static Logger LOG = LoggerFactory.getLogger(Engine.class); + + /** + * Starts the engine. + */ + public void start() { + LOG.info("Engine is starting!"); + } + + /** + * Stops the engine. + */ + public void stop() { + LOG.info("Engine is stopping!"); + } +} diff --git a/core-java/src/main/java/com/baeldung/designpatterns/flyweight/Vehicle.java b/core-java/src/main/java/com/baeldung/designpatterns/flyweight/Vehicle.java new file mode 100644 index 0000000000..c285f9fcff --- /dev/null +++ b/core-java/src/main/java/com/baeldung/designpatterns/flyweight/Vehicle.java @@ -0,0 +1,29 @@ +package com.baeldung.designpatterns.flyweight; + +import java.awt.Color; + +/** + * Interface for a vehicle. + * + * @author Donato Rimenti + */ +public interface Vehicle { + + /** + * Starts the vehicle. + */ + public void start(); + + /** + * Stops the vehicle. + */ + public void stop(); + + /** + * Gets the color of the vehicle. + * + * @return the color of the vehicle + */ + public Color getColor(); + +} \ No newline at end of file diff --git a/core-java/src/main/java/com/baeldung/designpatterns/flyweight/VehicleFactory.java b/core-java/src/main/java/com/baeldung/designpatterns/flyweight/VehicleFactory.java new file mode 100644 index 0000000000..2854b7dab1 --- /dev/null +++ b/core-java/src/main/java/com/baeldung/designpatterns/flyweight/VehicleFactory.java @@ -0,0 +1,45 @@ +package com.baeldung.designpatterns.flyweight; + +import java.awt.Color; +import java.util.HashMap; +import java.util.Map; + +/** + * Factory which implements the Flyweight pattern to return an existing vehicle + * if present or a new one otherwise. + * + * @author Donato Rimenti + */ +public class VehicleFactory { + + /** + * Stores the already created vehicles. + */ + private static Map vehiclesCache = new HashMap(); + + /** + * Private constructor to prevent this class instantiation. + */ + private VehicleFactory() { + } + + /** + * Returns a vehicle of the same color passed as argument. If that vehicle + * was already created by this factory, that vehicle is returned, otherwise + * a new one is created and returned. + * + * @param color + * the color of the vehicle to return + * @return a vehicle of the specified color + */ + public static Vehicle createVehicle(Color color) { + // Looks for the requested vehicle into the cache. + // If the vehicle doesn't exist, a new one is created. + Vehicle newVehicle = vehiclesCache.computeIfAbsent(color, newColor -> { + // Creates the new car. + Engine newEngine = new Engine(); + return new Car(newEngine, newColor); + }); + return newVehicle; + } +} diff --git a/core-java/src/test/java/com/baeldung/designpatterns/flyweight/FlyweightUnitTest.java b/core-java/src/test/java/com/baeldung/designpatterns/flyweight/FlyweightUnitTest.java new file mode 100644 index 0000000000..645e2fd459 --- /dev/null +++ b/core-java/src/test/java/com/baeldung/designpatterns/flyweight/FlyweightUnitTest.java @@ -0,0 +1,42 @@ +package com.baeldung.designpatterns.flyweight; + +import java.awt.Color; + +import org.junit.Assert; +import org.junit.Test; + +/** + * Unit test for {@link VehicleFactory}. + * + * @author Donato Rimenti + */ +public class FlyweightUnitTest { + + /** + * Checks that when the {@link VehicleFactory} is asked to provide two + * vehicles of different colors, the objects returned are different. + */ + @Test + public void givenDifferentFlyweightObjects_whenEquals_thenFalse() { + Vehicle blackVehicle = VehicleFactory.createVehicle(Color.BLACK); + Vehicle blueVehicle = VehicleFactory.createVehicle(Color.BLUE); + + Assert.assertNotNull("Object returned by the factory is null!", blackVehicle); + Assert.assertNotNull("Object returned by the factory is null!", blueVehicle); + Assert.assertNotEquals("Objects returned by the factory are equals!", blackVehicle, blueVehicle); + } + + /** + * Checks that when the {@link VehicleFactory} is asked to provide two + * vehicles of the same colors, the same object is returned twice. + */ + @Test + public void givenSameFlyweightObjects_whenEquals_thenTrue() { + Vehicle blackVehicle = VehicleFactory.createVehicle(Color.BLACK); + Vehicle anotherBlackVehicle = VehicleFactory.createVehicle(Color.BLACK); + + Assert.assertNotNull("Object returned by the factory is null!", blackVehicle); + Assert.assertNotNull("Object returned by the factory is null!", anotherBlackVehicle); + Assert.assertEquals("Objects returned by the factory are not equals!", blackVehicle, anotherBlackVehicle); + } +}