#554: Subclass Sandbox pattern (#998)

* Fix issue #761: ThreadSafeDoubleCheckLocking.java: Instantiating by Reflection call will be successful if you do that firstly

* Create leader election module

* Create Interface of Instance and MessageManager

* Create implementations with token ring algorithm

* Change package structure.
Create basic message system.

* Implement heartbeat and heartbeat invoking message system

* Implement election message handler

* Add leader message handler

* Add main entry point

* Add comments

* Update README.md

* Fix checkstyle issue

* Add Unit Tests

* Add Unit Tests

* Add bully leader selection

* Change System.out to log print.
Add MIT license in each file.

* Add More java doc comments

* Add unit test

* Add unit tests

* Add subclass-sandbox

* Add Unit Test

* Add Unit Test

* Fix Typo

* Move dependency into parent pom.xml

* Change local valuable reference to be var

pom.xml

@@ -60,6 +60,7 @@
         <jaxb-api.version>2.3.1</jaxb-api.version>
         <jaxb-impl.version>2.3.2</jaxb-impl.version>
         <annotation-api.version>1.3.2</annotation-api.version>
+        <system-rules.version>1.19.0</system-rules.version>
     </properties>
     <modules>
         <module>abstract-factory</module>
@@ -180,8 +181,8 @@
         <module>bytecode</module>
         <module>leader-election</module>
         <module>data-locality</module>
+        <module>subclass-sandbox</module>
         <module>circuit-breaker</module>
-
     </modules>
 
     <repositories>
@@ -317,6 +318,12 @@
                 <artifactId>javassist</artifactId>
                 <version>3.25.0-GA</version>
             </dependency>
+            <dependency>
+                <groupId>com.github.stefanbirkner</groupId>
+                <artifactId>system-rules</artifactId>
+                <version>${system-rules.version}</version>
+                <scope>test</scope>
+            </dependency>
         </dependencies>
     </dependencyManagement>
 

subclass-sandbox/README.md

@@ -0,0 +1,29 @@
+
+---  
+layout: pattern  
+title: Subclass Sandbox 
+folder:  subclass-sandbox  
+permalink: /patterns/subclass-sandbox/  
+categories: Other  
+tags:  
+ - Java  
+ - Difficulty-Beginner  
+---  
+
+## Intent  
+The subclass sandbox pattern describes a basic idea, while not having a lot of detailed mechanics. You will need the pattern when you have several similar subclasses. If you have to make a tiny change, then change the base class, while all subclasses shouldn't have to be touched. So the base class has to be able to provide all of the operations a derived class needs to perform.
+
+## Applicability  
+The Subclass Sandbox pattern is a very simple, common pattern lurking in lots of codebases, even outside of games. If you have a non-virtual protected method laying around, you’re probably already using something like this. Subclass Sandbox is a good fit when:
+
+-   You have a base class with a number of derived classes.
+
+-   The base class is able to provide all of the operations that a derived class may need to perform.
+
+-   There is behavioral overlap in the subclasses and you want to make it easier to share code between them.
+
+-   You want to minimize coupling between those derived classes and the rest of the program.
+
+## Credits  
+
+* [Game Programming Patterns - Subclass Sandbox]([http://gameprogrammingpatterns.com/subclass-sandbox.html](http://gameprogrammingpatterns.com/subclass-sandbox.html))

subclass-sandbox/pom.xml

@@ -0,0 +1,49 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+
+    The MIT License
+    Copyright ? 2014 Ilkka Sepp?l?
+
+    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.
+
+-->
+<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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <parent>
+        <artifactId>java-design-patterns</artifactId>
+        <groupId>com.iluwatar</groupId>
+        <version>1.22.0-SNAPSHOT</version>
+    </parent>
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>subclass-sandbox</artifactId>
+
+    <dependencies>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>com.github.stefanbirkner</groupId>
+            <artifactId>system-rules</artifactId>
+        </dependency>
+    </dependencies>
+
+</project>

subclass-sandbox/src/main/java/com/iluwatar/subclasssandbox/App.java

@@ -0,0 +1,53 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 Ilkka Seppälä
+ * <p>
+ * 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:
+ * <p>
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * <p>
+ * 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.subclasssandbox;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * The subclass sandbox pattern describes a basic idea, while not having a lot
+ * of detailed mechanics. You will need the pattern when you have several similar
+ * subclasses. If you have to make a tiny change, then change the base class,
+ * while all subclasses shouldn't have to be touched. So the base class has to be
+ * able to provide all of the operations a derived class needs to perform.
+ */
+public class App {
+
+  private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
+
+  /**
+   * Entry point of the main program.
+   * @param args Program runtime arguments.
+   */
+  public static void main(String[] args) {
+    LOGGER.info("Use superpower: sky launch");
+    var skyLaunch = new SkyLaunch();
+    skyLaunch.activate();
+    LOGGER.info("Use superpower: ground dive");
+    var groundDive = new GroundDive();
+    groundDive.activate();
+  }
+
+}

subclass-sandbox/src/main/java/com/iluwatar/subclasssandbox/GroundDive.java

@@ -0,0 +1,44 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 Ilkka Seppälä
+ * <p>
+ * 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:
+ * <p>
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * <p>
+ * 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.subclasssandbox;
+
+import org.slf4j.LoggerFactory;
+
+/**
+ * GroundDive superpower.
+ */
+public class GroundDive extends Superpower {
+
+  public GroundDive() {
+    super();
+    logger = LoggerFactory.getLogger(GroundDive.class);
+  }
+
+  @Override
+  protected void activate() {
+    move(0, 0, -20);
+    playSound("GROUNDDIVE_SOUND", 5);
+    spawnParticles("GROUNDDIVE_PARTICLE", 20);
+  }
+}

subclass-sandbox/src/main/java/com/iluwatar/subclasssandbox/SkyLaunch.java

@@ -0,0 +1,44 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 Ilkka Seppälä
+ * <p>
+ * 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:
+ * <p>
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * <p>
+ * 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.subclasssandbox;
+
+import org.slf4j.LoggerFactory;
+
+/**
+ * SkyLaunch superpower.
+ */
+public class SkyLaunch extends Superpower {
+
+  public SkyLaunch() {
+    super();
+    logger = LoggerFactory.getLogger(SkyLaunch.class);
+  }
+
+  @Override
+  protected void activate() {
+    move(0, 0, 20);
+    playSound("SKYLAUNCH_SOUND", 1);
+    spawnParticles("SKYLAUNCH_PARTICLE", 100);
+  }
+}

subclass-sandbox/src/main/java/com/iluwatar/subclasssandbox/Superpower.java

@@ -0,0 +1,69 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 Ilkka Seppälä
+ * <p>
+ * 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:
+ * <p>
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * <p>
+ * 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.subclasssandbox;
+
+import org.slf4j.Logger;
+
+/**
+ * Superpower abstract class. In this class the basic operations of all types of
+ * superpowers are provided as protected methods.
+ */
+public abstract class Superpower {
+
+  protected Logger logger;
+
+  /**
+   * Subclass of superpower should implement this sandbox method by calling the
+   * methods provided in this super class.
+   */
+  protected abstract void activate();
+
+  /**
+   * Move to (x, y, z).
+   * @param x X coordinate.
+   * @param y Y coordinate.
+   * @param z Z coordinate.
+   */
+  protected void move(double x, double y, double z) {
+    logger.info("Move to ( " + x + ", " + y + ", " + z + " )");
+  }
+
+  /**
+   * Play sound effect for the superpower.
+   * @param soundName Sound name.
+   * @param volumn Value of volumn.
+   */
+  protected void playSound(String soundName, int volumn) {
+    logger.info("Play " + soundName + " with volumn " + volumn);
+  }
+
+  /**
+   * Spawn particles for the superpower.
+   * @param particleType Particle type.
+   * @param count Count of particles to be spawned.
+   */
+  protected void spawnParticles(String particleType, int count) {
+    logger.info("Spawn " + count + " particle with type " + particleType);
+  }
+}

subclass-sandbox/src/test/java/com/iluwatar/subclasssandbox/AppTest.java

@@ -0,0 +1,38 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 Ilkka Seppälä
+ * <p>
+ * 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:
+ * <p>
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * <p>
+ * 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.subclasssandbox;
+
+import org.junit.Test;
+
+/**
+ * App unit tests.
+ */
+public class AppTest {
+
+  @Test
+  public void testMain() {
+    String[] args = {};
+    App.main(args);
+  }
+}