add singleton case

src/main/java/io/github/ehlxr/singleton/SingleEnum.java

@@ -0,0 +1,52 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright © 2020 xrv <xrg@live.com>
+ *
+ * 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 io.github.ehlxr.singleton;
+
+import java.util.stream.IntStream;
+
+/**
+ * 枚举单例模式
+ *
+ * @author ehlxr
+ * @since 2021-02-18 10:28.
+ */
+public enum SingleEnum {
+    /**
+     * 唯一实例
+     */
+    INSTANCE;
+
+    public static SingleEnum getInstance() {
+        return INSTANCE;
+    }
+
+    public String hello(String str) {
+        return "hello " + str;
+    }
+
+    public static void main(String[] args) {
+        IntStream.range(0, 5).parallel().forEach(i -> System.out.println(Thread.currentThread().getName() + " => " + SingleEnum.getInstance()));
+    }
+}

src/main/java/io/github/ehlxr/singleton/SingleTonStaticInnerClass.java

@@ -0,0 +1,49 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright © 2020 xrv <xrg@live.com>
+ *
+ * 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 io.github.ehlxr.singleton;
+
+import java.util.stream.IntStream;
+
+/**
+ * @author ehlxr
+ * @since 2021-02-18 11:23.
+ */
+public class SingleTonStaticInnerClass {
+    private SingleTonStaticInnerClass() {
+    }
+
+    private static class HandlerInstance {
+        private static SingleTonStaticInnerClass instance = new SingleTonStaticInnerClass();
+    }
+
+    public static SingleTonStaticInnerClass getInstance() {
+        return HandlerInstance.instance;
+    }
+
+    public static void main(String[] args) {
+        IntStream.range(0, 5).parallel().forEach(i -> System.out.println(Thread.currentThread().getName() + " => " + SingleTonStaticInnerClass.getInstance()));
+    }
+
+}

src/main/java/io/github/ehlxr/singleton/SingletonDcl.java

@@ -0,0 +1,69 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright © 2020 xrv <xrg@live.com>
+ *
+ * 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 io.github.ehlxr.singleton;
+
+import java.lang.reflect.Constructor;
+import java.util.stream.IntStream;
+
+/**
+ * double check lock
+ * <p>
+ * 懒汉模式
+ *
+ * @author ehlxr
+ * @since 2021-02-18 10:23.
+ */
+public class SingletonDcl {
+    private SingletonDcl() {
+    }
+
+    private volatile static SingletonDcl INSTANCE;
+
+    public static SingletonDcl getInstance() {
+        if (INSTANCE == null) {
+            synchronized (SingletonDcl.class) {
+                if (INSTANCE == null) {
+                    // 非原子性操作
+                    // 有可能会出现 JVM 优化指令重排序
+                    INSTANCE = new SingletonDcl();
+                }
+            }
+        }
+
+        return INSTANCE;
+    }
+
+    public static void main(String[] args) throws Exception {
+        IntStream.range(0, 5).parallel().forEach(i -> System.out.println(Thread.currentThread().getName() + " => " + SingletonDcl.getInstance()));
+
+        // 反射破坏
+        Constructor<SingletonDcl> dc = SingletonDcl.class.getDeclaredConstructor();
+        dc.setAccessible(true);
+
+        System.out.println(dc.newInstance());
+        System.out.println(dc.newInstance());
+        System.out.println(dc.newInstance());
+    }
+}

src/main/java/io/github/ehlxr/singleton/SingletonHungry.java

@@ -0,0 +1,72 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright © 2020 xrv <xrg@live.com>
+ *
+ * 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 io.github.ehlxr.singleton;
+
+import java.io.*;
+import java.util.stream.IntStream;
+
+/**
+ * 饿汉模式
+ *
+ * @author ehlxr
+ * @since 2021-02-18 10:20.
+ */
+public class SingletonHungry implements Serializable {
+    private static final long serialVersionUID = -3654446367492818614L;
+
+    private SingletonHungry() {
+    }
+
+    private static final SingletonHungry INSTANCE = new SingletonHungry();
+
+    public static SingletonHungry getInstance() {
+        return INSTANCE;
+    }
+
+    // 防止 jdk 反序列化破坏单例
+    private Object readResolve() {
+        return INSTANCE;
+    }
+
+    public static void main(String[] args) throws Exception{
+        IntStream.range(0, 5).parallel().forEach(i -> System.out.println(Thread.currentThread().getName() + " => " + SingleTonStaticInnerClass.getInstance()));
+
+        // 序列化破坏
+        SingletonHungry instance = SingletonHungry.getInstance();
+        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("singleton_file"));
+        // 序列化【写】操作
+        oos.writeObject(instance);
+        File file = new File("singleton_file");
+        ObjectInputStream ois = new ObjectInputStream(new FileInputStream(file));
+
+        // 反序列化【读】操作
+        SingletonHungry newInstance = (SingletonHungry) ois.readObject();
+        System.out.println(instance);
+        System.out.println(newInstance);
+        System.out.println(instance == newInstance);
+
+    }
+
+}