小傅哥 | 重学 Java 设计模式：实战单例模式

.gitignore

@@ -9,3 +9,5 @@
 /itstack-demo-desgin-4-01/itstack-demo-desgin-4-01.iml
 /itstack-demo-design-4-02/itstack-demo-design-4-02.iml
 /itstack-demo-design-4-00/itstack-demo-design-4-00.iml
+/itstack-demo-design-5-00/itstack-demo-design-5-00.iml
+/itstack-demo-design-5-01/itstack-demo-design-5-01.iml

itstack-demo-design-5-00/pom.xml

+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <parent>
+        <artifactId>itstack-demo-design</artifactId>
+        <groupId>org.itstack</groupId>
+        <version>1.0-SNAPSHOT</version>
+    </parent>
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>itstack-demo-design-5-00</artifactId>
+
+
+</project>
\ No newline at end of file

itstack-demo-design-5-00/src/main/java/org/itstack/demo/design/Singleton_00.java

+package org.itstack.demo.design;
+
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+public class Singleton_00 {
+
+    public static Map<String,String> cache = new ConcurrentHashMap<String, String>();
+
+}

itstack-demo-design-5-00/src/main/java/org/itstack/demo/design/Singleton_01.java

+package org.itstack.demo.design;
+
+public class Singleton_01 {
+
+    private static Singleton_01 instance;
+
+    private Singleton_01() {
+    }
+
+    public static Singleton_01 getInstance(){
+        if (null != instance) return instance;
+        return new Singleton_01();
+    }
+
+}

itstack-demo-design-5-00/src/main/java/org/itstack/demo/design/Singleton_02.java

+package org.itstack.demo.design;
+
+public class Singleton_02 {
+
+    private static Singleton_02 instance;
+
+    private Singleton_02() {
+    }
+
+    public static synchronized Singleton_02 getInstance(){
+        if (null != instance) return instance;
+        return new Singleton_02();
+    }
+
+}

itstack-demo-design-5-00/src/main/java/org/itstack/demo/design/Singleton_03.java

+package org.itstack.demo.design;
+
+public class Singleton_03 {
+
+    private static Singleton_03 instance = new Singleton_03();
+
+    private Singleton_03() {
+    }
+
+    public static Singleton_03 getInstance() {
+        return instance;
+    }
+
+}

itstack-demo-design-5-00/src/main/java/org/itstack/demo/design/Singleton_04.java

+package org.itstack.demo.design;
+
+public class Singleton_04 {
+
+    private static class SingletonHolder {
+        private static Singleton_04 instance = new Singleton_04();
+    }
+
+    private Singleton_04() {
+    }
+
+    public static Singleton_04 getInstance() {
+        return SingletonHolder.instance;
+    }
+
+}

itstack-demo-design-5-00/src/main/java/org/itstack/demo/design/Singleton_05.java

+package org.itstack.demo.design;
+
+public class Singleton_05 {
+
+    private static Singleton_05 instance;
+
+    private Singleton_05() {
+    }
+
+    public static Singleton_05 getInstance(){
+       if(null != instance) return instance;
+       synchronized (Singleton_05.class){
+           if (null == instance){
+               instance = new Singleton_05();
+           }
+       }
+       return instance;
+    }
+
+}

itstack-demo-design-5-00/src/main/java/org/itstack/demo/design/Singleton_06.java

+package org.itstack.demo.design;
+
+import java.util.concurrent.atomic.AtomicReference;
+
+public class Singleton_06 {
+
+    private static final AtomicReference<Singleton_06> INSTANCE = new AtomicReference<Singleton_06>();
+
+    private static Singleton_06 instance;
+
+    private Singleton_06() {
+    }
+
+    public static final Singleton_06 getInstance() {
+        for (; ; ) {
+            Singleton_06 instance = INSTANCE.get();
+            if (null != instance) return instance;
+            INSTANCE.compareAndSet(null, new Singleton_06());
+            return INSTANCE.get();
+        }
+    }
+
+    public static void main(String[] args) {
+        System.out.println(Singleton_06.getInstance()); // org.itstack.demo.design.Singleton_06@2b193f2d
+        System.out.println(Singleton_06.getInstance()); // org.itstack.demo.design.Singleton_06@2b193f2d
+    }
+
+
+}

itstack-demo-design-5-00/src/main/java/org/itstack/demo/design/Singleton_07.java

+package org.itstack.demo.design;
+
+public enum Singleton_07 {
+
+    INSTANCE;
+    public void test(){
+        System.out.println("hi~");
+    }
+
+}

itstack-demo-design-5-00/src/test/java/org/itstack/demo/design/test/ApiTest.java

+package org.itstack.demo.design.test;
+
+import org.itstack.demo.design.Singleton_00;
+import org.itstack.demo.design.Singleton_07;
+import org.junit.Test;
+
+public class ApiTest {
+
+    @Test
+    public void test() {
+        Singleton_07.INSTANCE.test();
+    }
+
+}

pom.xml

@@ -21,6 +21,7 @@
         <module>itstack-demo-design-4-00</module>
         <module>itstack-demo-desgin-4-01</module>
         <module>itstack-demo-design-4-02</module>
+        <module>itstack-demo-design-5-00</module>
     </modules>
 
     <dependencies>