update singleton design pattern

Author: delei

source/java/interview/delei-interview-designpattern/src/main/java/cn/delei/designpattern/singleton/DoubleCheckLockSingleton.java

@@ -0,0 +1,28 @@
+package cn.delei.designpattern.singleton;
+
+/**
+ * 双重锁机制
+ * <p>volatile结合synchronized关键字,线程安全</p>
+ *
+ * @author deleiguo
+ */
+public class DoubleCheckLockSingleton {
+    
+    private volatile static DoubleCheckLockSingleton instance;
+
+    private DoubleCheckLockSingleton() {}
+
+    public static DoubleCheckLockSingleton getInstance() {
+        // 检查是否要阻塞
+        if (instance == null) {
+            // 为类(对象)加锁
+            synchronized (DoubleCheckLockSingleton.class) {
+                // 检查是否要重新创建实例
+                if (instance == null) {
+                    instance = new DoubleCheckLockSingleton();
+                }
+            }
+        }
+        return instance;
+    }
+}

source/java/interview/delei-interview-designpattern/src/main/java/cn/delei/designpattern/singleton/Singleton_7.java renamed to source/java/interview/delei-interview-designpattern/src/main/java/cn/delei/designpattern/singleton/EnumSingleton.java

@@ -6,18 +6,18 @@
  *
  * @author deleiguo
  */
-public class Singleton_7 {
+public class EnumSingleton {
 
     static enum SingletonEnum {
         INSTANCE;
 
-        private Singleton_7 singleton;
+        private EnumSingleton singleton;
 
         private SingletonEnum() {
-            singleton = new Singleton_7();
+            singleton = new EnumSingleton();
         }
 
-        public Singleton_7 getInstnce() {
+        public EnumSingleton getInstnce() {
             return singleton;
         }
     }
@@ -27,7 +27,7 @@ public Singleton_7 getInstnce() {
      *
      * @return Singleton_6 实例
      */
-    public static Singleton_7 getInstance() {
+    public static EnumSingleton getInstance() {
         return SingletonEnum.INSTANCE.getInstnce();
     }
 }

source/java/interview/delei-interview-designpattern/src/main/java/cn/delei/designpattern/singleton/EnumSingletonWithData.java

@@ -0,0 +1,23 @@
+package cn.delei.designpattern.singleton;
+
+/**
+ * 使用枚举来实现单实例控制
+ * 无偿地提供了序列化机制，并由JVM从根本上提供保障，绝对防止多次实例化
+ *
+ * @author deleiguo
+ */
+public enum EnumSingletonWithData {
+    INSTANCE;
+
+    private Object data;
+
+    public Object getData() {
+        return data;
+    }
+
+    public void setData(Object data) {
+        this.data = data;
+    }
+
+    public static EnumSingletonWithData getInstance(){return INSTANCE;}
+}

source/java/interview/delei-interview-designpattern/src/main/java/cn/delei/designpattern/singleton/HungryNormalSingleton.java

@@ -0,0 +1,18 @@
+package cn.delei.designpattern.singleton;
+
+/**
+ * 饿汉式
+ * <p>java classloader类加载时就初始化，线程安全,no lazy loading</p>
+ *
+ * @author deleiguo
+ */
+public class HungryNormalSingleton {
+    private static HungryNormalSingleton instance = new HungryNormalSingleton();
+
+    public HungryNormalSingleton() {
+    }
+
+    public static HungryNormalSingleton getInstance() {
+        return instance;
+    }
+}

source/java/interview/delei-interview-designpattern/src/main/java/cn/delei/designpattern/singleton/HungryNormalStaticSingleton.java

@@ -0,0 +1,21 @@
+package cn.delei.designpattern.singleton;
+
+/**
+ * 饿汉式
+ * <p>java classloader类加载时就初始化，线程安全,no lazy loading</p>
+ *
+ * @author deleiguo
+ */
+public class HungryNormalStaticSingleton {
+    private static final HungryNormalStaticSingleton instance;
+
+    static {
+        instance = new HungryNormalStaticSingleton();
+    }
+
+    public HungryNormalStaticSingleton() {}
+
+    public static HungryNormalStaticSingleton getInstance() {
+        return instance;
+    }
+}

source/java/interview/delei-interview-designpattern/src/main/java/cn/delei/designpattern/singleton/LazyNormalSingleton.java

@@ -0,0 +1,22 @@
+package cn.delei.designpattern.singleton;
+
+/**
+ * 懒汉式
+ * <p>lazy loading 支持多线程，但是同步效率低</p>
+ *
+ * @author deleiguo
+ */
+public class LazyNormalSingleton {
+    private static LazyNormalSingleton instance;
+
+    private LazyNormalSingleton() {
+
+    }
+
+    public static synchronized LazyNormalSingleton getInstance() {
+        if (instance == null) {
+            instance = new LazyNormalSingleton();
+        }
+        return instance;
+    }
+}

source/java/interview/delei-interview-designpattern/src/main/java/cn/delei/designpattern/singleton/LazyNormalUnSafeSingleton.java

@@ -0,0 +1,21 @@
+package cn.delei.designpattern.singleton;
+
+/**
+ * 基本实现方式
+ * <p>不支持多线程 非线程安全 lazy loading</p>
+ *
+ * @author deleiguo
+ */
+public class LazyNormalUnSafeSingleton {
+    // 静态块，公共内存区域
+    private static LazyNormalUnSafeSingleton instance;
+
+    private LazyNormalUnSafeSingleton() {}
+
+    public static LazyNormalUnSafeSingleton getInstance() {
+        if (instance == null) {
+            instance = new LazyNormalUnSafeSingleton();
+        }
+        return instance;
+    }
+}