singleton

Author: code4craft

src/main/java/helloworld/Main.java

@@ -5,6 +5,7 @@
 import helloworld.creational.builder.HelloWorldBuilder;
 import helloworld.creational.factory_method.FactoryMethodHelloWorldFactory;
 import helloworld.creational.prototype.HelloWorldPrototype;
+import helloworld.creational.singleton.HelloWorldSingleton;
 
 /**
  * @author yihua.huang@dianping.com
@@ -35,5 +36,8 @@ public static void main(String[] args) throws InstantiationException, IllegalAcc
         HelloWorld prototypeHelloWorld = HelloWorldPrototype.PROTOTYPE.clone();
         System.out.println(prototypeHelloWorld.helloWorld());
 
+        HelloWorld singletonHelloWorld = HelloWorldSingleton.instance();
+        System.out.println(singletonHelloWorld.helloWorld());
+
     }
 }

src/main/java/helloworld/creational/singleton/HelloWorldSingleton.java

@@ -0,0 +1,27 @@
+package helloworld.creational.singleton;
+
+import helloworld.HelloWorld;
+
+/**
+ * @author yihua.huang@dianping.com
+ */
+public class HelloWorldSingleton implements HelloWorld {
+
+    @Override
+    public String helloWorld() {
+        return "Hello Singleton!";
+    }
+
+    public static HelloWorldSingleton instance() {
+        return HelloWorldSingletonInner.INSTANCE;
+    }
+
+    private HelloWorldSingleton() {
+
+    }
+
+    static class HelloWorldSingletonInner {
+        private static final HelloWorldSingleton INSTANCE = new HelloWorldSingleton();
+    }
+
+}

src/test/java/helloworld/creational/singleton/HelloWorldSingletonTest.java

@@ -0,0 +1,18 @@
+package helloworld.creational.singleton;
+
+import helloworld.HelloWorld;
+import org.junit.Test;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.is;
+
+/**
+ * @author yihua.huang@dianping.com
+ */
+public class HelloWorldSingletonTest {
+
+    @Test
+    public void testHelloWorldSingleton(){
+        HelloWorld helloWorld = HelloWorldSingleton.instance();
+        assertThat(helloWorld.helloWorld(),is("Hello Singleton!"));
+    }
+}