🍻 罗列所有的单例模式

netty-design-patterns-singleton/src/main/java/cn/mushuwei/singleton/App.java

@@ -1,7 +1,6 @@
 package cn.mushuwei.singleton;
 
-import cn.mushuwei.singleton.type.MouseDriver;
-import cn.mushuwei.singleton.type.ThreadSafeLazyLoadedMouseDriver;
+import cn.mushuwei.singleton.type.*;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -22,9 +21,27 @@ public static void main(String[] args) {
         LOGGER.info("mouseDriver2={}", mouseDriver2);
 
         // lazily initialized singleton
-        ThreadSafeLazyLoadedMouseDriver threadSafeIvoryTower1 = ThreadSafeLazyLoadedMouseDriver.getInstance();
-        ThreadSafeLazyLoadedMouseDriver threadSafeIvoryTower2 = ThreadSafeLazyLoadedMouseDriver.getInstance();
-        LOGGER.info("threadSafeIvoryTower1={}", threadSafeIvoryTower1);
-        LOGGER.info("threadSafeIvoryTower2={}", threadSafeIvoryTower2);
+        ThreadSafeLazyLoadedMouseDriver threadSafeMouseDriver1 = ThreadSafeLazyLoadedMouseDriver.getInstance();
+        ThreadSafeLazyLoadedMouseDriver threadSafeMouseDriver2 = ThreadSafeLazyLoadedMouseDriver.getInstance();
+        LOGGER.info("threadSafeMouseDriver1={}", threadSafeMouseDriver1);
+        LOGGER.info("threadSafeMouseDriver2={}", threadSafeMouseDriver2);
+
+        // enum singleton
+        EnumMouseDriver enumMouseDriver1 = EnumMouseDriver.INSTANCE;
+        EnumMouseDriver enumMouseDriver2 = EnumMouseDriver.INSTANCE;
+        LOGGER.info("enumMouseDriver1={}", enumMouseDriver1);
+        LOGGER.info("enumMouseDriver2={}", enumMouseDriver2);
+
+        // double checked locking
+        ThreadSafeDoubleCheckLocking dcl1 = ThreadSafeDoubleCheckLocking.getInstance();
+        LOGGER.info(dcl1.toString());
+        ThreadSafeDoubleCheckLocking dcl2 = ThreadSafeDoubleCheckLocking.getInstance();
+        LOGGER.info(dcl2.toString());
+
+        // initialize on demand holder idiom
+        InitializingOnDemandHolderIdiom demandHolderIdiom = InitializingOnDemandHolderIdiom.getInstance();
+        LOGGER.info(demandHolderIdiom.toString());
+        InitializingOnDemandHolderIdiom demandHolderIdiom2 = InitializingOnDemandHolderIdiom.getInstance();
+        LOGGER.info(demandHolderIdiom2.toString());
     }
 }

netty-design-patterns-singleton/src/main/java/cn/mushuwei/singleton/type/EnumMouseDriver.java

@@ -0,0 +1,18 @@
+package cn.mushuwei.singleton.type;
+
+/**
+ * 基于枚举的单例实现, Effective Java 中文第二版(Joshua Bloch) p.15
+ * 此实现是线程安全的，但是添加任何其他方法及其线程安全是开发人员的责任
+ *
+ * @author james mu
+ * @date 2020/4/14 09:01
+ */
+public enum  EnumMouseDriver {
+
+    INSTANCE;
+
+    @Override
+    public String toString(){
+        return getDeclaringClass().getCanonicalName() + "@" + hashCode();
+    }
+}

netty-design-patterns-singleton/src/main/java/cn/mushuwei/singleton/type/InitializingOnDemandHolderIdiom.java

@@ -0,0 +1,20 @@
+package cn.mushuwei.singleton.type;
+
+/**
+ * @author james mu
+ * @date 2020/4/14 09:12
+ */
+public final class InitializingOnDemandHolderIdiom {
+
+    private InitializingOnDemandHolderIdiom() {
+    }
+
+    public static InitializingOnDemandHolderIdiom getInstance() {
+        return HelperHolder.INSTANCE;
+    }
+
+    private static class HelperHolder {
+        private static final InitializingOnDemandHolderIdiom INSTANCE =
+                new InitializingOnDemandHolderIdiom();
+    }
+}

netty-design-patterns-singleton/src/main/java/cn/mushuwei/singleton/type/ThreadSafeDoubleCheckLocking.java

@@ -0,0 +1,24 @@
+package cn.mushuwei.singleton.type;
+
+/**
+ * @author james mu
+ * @date 2020/4/14 09:34
+ */
+public class ThreadSafeDoubleCheckLocking {
+
+    private volatile static ThreadSafeDoubleCheckLocking uniqueInstance;
+
+    private ThreadSafeDoubleCheckLocking() {
+    }
+
+    public static ThreadSafeDoubleCheckLocking getInstance() {
+        if (uniqueInstance == null) {
+            synchronized (ThreadSafeDoubleCheckLocking.class) {
+                if (uniqueInstance == null) {
+                    uniqueInstance = new ThreadSafeDoubleCheckLocking();
+                }
+            }
+        }
+        return uniqueInstance;
+    }
+}