Adding design pattern examples.

.gitignore

@@ -29,3 +29,5 @@ Existing
 hs_err_pid*
 
 # End of https://www.gitignore.io/api/java
+
+target/

code-samples/03-Design-Patterns/01-singleton/pom.xml

@@ -0,0 +1,75 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<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">
+  <modelVersion>4.0.0</modelVersion>
+
+  <groupId>com.algogrit.java</groupId>
+  <artifactId>singleton</artifactId>
+  <version>1.0-SNAPSHOT</version>
+
+  <name>singleton</name>
+  <!-- FIXME change it to the project's website -->
+  <url>http://www.example.com</url>
+
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <maven.compiler.source>1.7</maven.compiler.source>
+    <maven.compiler.target>1.7</maven.compiler.target>
+  </properties>
+
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <version>4.11</version>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+
+  <build>
+    <pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
+      <plugins>
+        <!-- clean lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#clean_Lifecycle -->
+        <plugin>
+          <artifactId>maven-clean-plugin</artifactId>
+          <version>3.1.0</version>
+        </plugin>
+        <!-- default lifecycle, jar packaging: see https://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_jar_packaging -->
+        <plugin>
+          <artifactId>maven-resources-plugin</artifactId>
+          <version>3.0.2</version>
+        </plugin>
+        <plugin>
+          <artifactId>maven-compiler-plugin</artifactId>
+          <version>3.8.0</version>
+        </plugin>
+        <plugin>
+          <artifactId>maven-surefire-plugin</artifactId>
+          <version>2.22.1</version>
+        </plugin>
+        <plugin>
+          <artifactId>maven-jar-plugin</artifactId>
+          <version>3.0.2</version>
+        </plugin>
+        <plugin>
+          <artifactId>maven-install-plugin</artifactId>
+          <version>2.5.2</version>
+        </plugin>
+        <plugin>
+          <artifactId>maven-deploy-plugin</artifactId>
+          <version>2.8.2</version>
+        </plugin>
+        <!-- site lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#site_Lifecycle -->
+        <plugin>
+          <artifactId>maven-site-plugin</artifactId>
+          <version>3.7.1</version>
+        </plugin>
+        <plugin>
+          <artifactId>maven-project-info-reports-plugin</artifactId>
+          <version>3.0.0</version>
+        </plugin>
+      </plugins>
+    </pluginManagement>
+  </build>
+</project>

code-samples/03-Design-Patterns/01-singleton/src/main/java/com/algogrit/java/App.java

@@ -0,0 +1,27 @@
+package com.algogrit.java;
+
+/**
+ * Hello world!
+ *
+ */
+public class App
+{
+    public static void main( String[] args )
+    {
+        // printerDriver.print("Hello World!");
+
+        System.out.println("Creating instance...");
+        PrinterDriver printerDriver1 = PrinterDriver.getInstance();
+
+        System.out.println("Fetching instance...");
+        PrinterDriver printerDriver2 = PrinterDriver.getInstance();
+
+        // ThreadSafeLazyLoadedIvoryTower ivoryTower = new ThreadSafeLazyLoadedIvoryTower();
+
+        // printerDriver.print("Hello World!");
+
+        System.out.println(PrinterDriver.class);
+
+        System.out.println("Hello world!");
+    }
+}

code-samples/03-Design-Patterns/01-singleton/src/main/java/com/algogrit/java/PrinterDriver.java

@@ -0,0 +1,27 @@
+package com.algogrit.java;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class PrinterDriver {
+  private List<Object> queue = new ArrayList<Object>();
+
+  private static PrinterDriver INSTANCE = new PrinterDriver();
+
+  public static PrinterDriver getInstance() {
+    return INSTANCE;
+  }
+
+  private PrinterDriver() {
+    System.out.println("Instance created!");
+  }
+
+  public void print(Object o) {
+    this.queue.add(o);
+    lazyPrint();
+  }
+
+  public void lazyPrint() {
+    System.out.println("I will lazily print the objects");
+  }
+}

code-samples/03-Design-Patterns/01-singleton/src/main/java/com/algogrit/java/ThreadSafeLazyLoadedIvoryTower.java

@@ -0,0 +1,51 @@
+/**
+ * The MIT License Copyright (c) 2014-2016 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.algogrit.java;
+
+/**
+ * Thread-safe Singleton class. The instance is lazily initialized and thus needs synchronization
+ * mechanism.
+ *
+ * Note: if created by reflection then a singleton will not be created but multiple options in the
+ * same classloader
+ */
+public final class ThreadSafeLazyLoadedIvoryTower {
+
+  private static ThreadSafeLazyLoadedIvoryTower instance;
+
+  private ThreadSafeLazyLoadedIvoryTower() {
+    // protect against instantiation via reflection
+    if (instance == null) {
+      instance = this;
+    } else {
+      throw new IllegalStateException("Already initialized.");
+    }
+  }
+
+  /**
+   * The instance gets created only when it is called for first time. Lazy-loading
+   */
+  public static synchronized ThreadSafeLazyLoadedIvoryTower getInstance() {
+    if (instance == null) {
+      instance = new ThreadSafeLazyLoadedIvoryTower();
+    }
+
+    return instance;
+  }
+}

code-samples/03-Design-Patterns/01-singleton/src/test/java/com/algogrit/java/AppTest.java

@@ -0,0 +1,20 @@
+package com.algogrit.java;
+
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+/**
+ * Unit test for simple App.
+ */
+public class AppTest 
+{
+    /**
+     * Rigorous Test :-)
+     */
+    @Test
+    public void shouldAnswerWithTrue()
+    {
+        assertTrue( true );
+    }
+}

code-samples/03-Design-Patterns/02-factory-method/pom.xml

@@ -0,0 +1,75 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<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">
+  <modelVersion>4.0.0</modelVersion>
+
+  <groupId>com.algogrit.java</groupId>
+  <artifactId>factory-method</artifactId>
+  <version>1.0-SNAPSHOT</version>
+
+  <name>factory-method</name>
+  <!-- FIXME change it to the project's website -->
+  <url>http://www.example.com</url>
+
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <maven.compiler.source>1.7</maven.compiler.source>
+    <maven.compiler.target>1.7</maven.compiler.target>
+  </properties>
+
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <version>4.11</version>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+
+  <build>
+    <pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
+      <plugins>
+        <!-- clean lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#clean_Lifecycle -->
+        <plugin>
+          <artifactId>maven-clean-plugin</artifactId>
+          <version>3.1.0</version>
+        </plugin>
+        <!-- default lifecycle, jar packaging: see https://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_jar_packaging -->
+        <plugin>
+          <artifactId>maven-resources-plugin</artifactId>
+          <version>3.0.2</version>
+        </plugin>
+        <plugin>
+          <artifactId>maven-compiler-plugin</artifactId>
+          <version>3.8.0</version>
+        </plugin>
+        <plugin>
+          <artifactId>maven-surefire-plugin</artifactId>
+          <version>2.22.1</version>
+        </plugin>
+        <plugin>
+          <artifactId>maven-jar-plugin</artifactId>
+          <version>3.0.2</version>
+        </plugin>
+        <plugin>
+          <artifactId>maven-install-plugin</artifactId>
+          <version>2.5.2</version>
+        </plugin>
+        <plugin>
+          <artifactId>maven-deploy-plugin</artifactId>
+          <version>2.8.2</version>
+        </plugin>
+        <!-- site lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#site_Lifecycle -->
+        <plugin>
+          <artifactId>maven-site-plugin</artifactId>
+          <version>3.7.1</version>
+        </plugin>
+        <plugin>
+          <artifactId>maven-project-info-reports-plugin</artifactId>
+          <version>3.0.0</version>
+        </plugin>
+      </plugins>
+    </pluginManagement>
+  </build>
+</project>

code-samples/03-Design-Patterns/02-factory-method/src/main/java/com/algogrit/java/App.java

@@ -0,0 +1,14 @@
+package com.algogrit.java;
+
+/**
+* Hello world!
+*
+*/
+public class App {
+    public static void main(String[] args) {
+        EngineerFactory engineerFactory = new CivilEngineerFactory();
+
+        Engineer engineer = engineerFactory.getEngineer();
+        engineer.work();
+    }
+}

code-samples/03-Design-Patterns/02-factory-method/src/main/java/com/algogrit/java/CivilEngineer.java

@@ -0,0 +1,8 @@
+package com.algogrit.java;
+
+public class CivilEngineer implements Engineer {
+	@Override
+	public void work() {
+		System.out.println("Does Construction");
+	}
+}

code-samples/03-Design-Patterns/02-factory-method/src/main/java/com/algogrit/java/CivilEngineerFactory.java

@@ -0,0 +1,7 @@
+package com.algogrit.java;
+
+public class CivilEngineerFactory implements EngineerFactory {
+  public Engineer getEngineer() {
+    return new CivilEngineer();
+  }
+}

code-samples/03-Design-Patterns/02-factory-method/src/main/java/com/algogrit/java/ComputerEngineer.java

@@ -0,0 +1,8 @@
+package com.algogrit.java;
+
+public class ComputerEngineer implements Engineer {
+	@Override
+	public void work() {
+		System.out.println("Does Software");
+  }
+}

code-samples/03-Design-Patterns/02-factory-method/src/main/java/com/algogrit/java/ComputerEngineerFactory.java

@@ -0,0 +1,7 @@
+package com.algogrit.java;
+
+public class ComputerEngineerFactory implements EngineerFactory {
+  public Engineer getEngineer() {
+    return new ComputerEngineer();
+  }
+}

code-samples/03-Design-Patterns/02-factory-method/src/main/java/com/algogrit/java/Engineer.java

@@ -0,0 +1,5 @@
+package com.algogrit.java;
+
+public interface Engineer {
+	public void work();
+}

code-samples/03-Design-Patterns/02-factory-method/src/main/java/com/algogrit/java/EngineerFactory.java

@@ -0,0 +1,5 @@
+package com.algogrit.java;
+
+interface EngineerFactory {
+  Engineer getEngineer();
+}

code-samples/03-Design-Patterns/02-factory-method/src/test/java/com/algogrit/java/AppTest.java

@@ -0,0 +1,20 @@
+package com.algogrit.java;
+
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+/**
+ * Unit test for simple App.
+ */
+public class AppTest 
+{
+    /**
+     * Rigorous Test :-)
+     */
+    @Test
+    public void shouldAnswerWithTrue()
+    {
+        assertTrue( true );
+    }
+}