Merge pull request iluwatar#724 from anthonycampbell/master

My solution to issue iluwatar#602.

Author: iluwatar

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

@@ -31,9 +31,12 @@
  * pattern defines many globally accessible objects. The client asks for the correct instance from
  * the Multiton by passing an enumeration as parameter.
  * <p>
- * In this example {@link Nazgul} is the Multiton and we can ask single {@link Nazgul} from it using
- * {@link NazgulName}. The {@link Nazgul}s are statically initialized and stored in concurrent hash
- * map.
+ * There is more than one way to implement the multiton design pattern. In the first example
+ * {@link Nazgul} is the Multiton and we can ask single {@link Nazgul} from it using {@link NazgulName}.
+ * The {@link Nazgul}s are statically initialized and stored in concurrent hash map.
+ * <p>
+ * In the enum implementation {@link NazgulEnum} is the multiton. It is static and mutable because
+ * of the way java supports enums.
  *
  */
 public class App {
@@ -46,6 +49,7 @@ public class App {
    * @param args command line args
    */
   public static void main(String[] args) {
+    // eagerly initialized multiton
     LOGGER.info("KHAMUL={}", Nazgul.getInstance(NazgulName.KHAMUL));
     LOGGER.info("MURAZOR={}", Nazgul.getInstance(NazgulName.MURAZOR));
     LOGGER.info("DWAR={}", Nazgul.getInstance(NazgulName.DWAR));
@@ -55,5 +59,16 @@ public static void main(String[] args) {
     LOGGER.info("ADUNAPHEL={}", Nazgul.getInstance(NazgulName.ADUNAPHEL));
     LOGGER.info("REN={}", Nazgul.getInstance(NazgulName.REN));
     LOGGER.info("UVATHA={}", Nazgul.getInstance(NazgulName.UVATHA));
+    
+    // enum multiton
+    LOGGER.info("KHAMUL={}", NazgulEnum.KHAMUL);
+    LOGGER.info("MURAZOR={}", NazgulEnum.MURAZOR);
+    LOGGER.info("DWAR={}", NazgulEnum.DWAR);
+    LOGGER.info("JI_INDUR={}", NazgulEnum.JI_INDUR);
+    LOGGER.info("AKHORAHIL={}", NazgulEnum.AKHORAHIL);
+    LOGGER.info("HOARMURATH={}", NazgulEnum.HOARMURATH);
+    LOGGER.info("ADUNAPHEL={}", NazgulEnum.ADUNAPHEL);
+    LOGGER.info("REN={}", NazgulEnum.REN);
+    LOGGER.info("UVATHA={}", NazgulEnum.UVATHA);
   }
 }

multiton/src/main/java/com/iluwatar/multiton/NazgulEnum.java

@@ -0,0 +1,33 @@
+/**
+ * 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.iluwatar.multiton;
+
+/**
+ * enum based multiton implementation
+ *
+ */
+public enum NazgulEnum {
+  
+  KHAMUL, MURAZOR, DWAR, JI_INDUR, AKHORAHIL, HOARMURATH, ADUNAPHEL, REN, UVATHA;
+
+}

multiton/src/test/java/com/iluwatar/multiton/NazgulEnumTest.java

@@ -0,0 +1,50 @@
+/**
+ * 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.iluwatar.multiton;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * @author anthony
+ *
+ */
+class NazgulEnumTest {
+
+  /**
+   * Check that multiple calls to any one of the instances in the multiton returns 
+   * only that one particular instance, and do that for all instances in multiton
+   */
+  @Test
+  public void testTheSameObjectIsReturnedWithMultipleCalls() {
+    for (int i = 0; i < NazgulEnum.values().length; i++) {
+      NazgulEnum instance1 = NazgulEnum.values()[i];
+      NazgulEnum instance2 = NazgulEnum.values()[i];
+      NazgulEnum instance3 = NazgulEnum.values()[i];
+      assertSame(instance1, instance2);
+      assertSame(instance1, instance3);
+      assertSame(instance2, instance3);
+    }
+  }
+}