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

@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http:https://maven.apache.org/POM/4.0.0"
+ xmlns:xsi="http:https://www.w3.org/2001/XMLSchema-instance"
+ xsi:schemaLocation="http:https://maven.apache.org/POM/4.0.0 http:https://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>

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

@@ -0,0 +1,10 @@
+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

@@ -0,0 +1,15 @@
+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

@@ -0,0 +1,15 @@
+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

@@ -0,0 +1,14 @@
+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

@@ -0,0 +1,16 @@
+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

@@ -0,0 +1,20 @@
+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

@@ -0,0 +1,29 @@
+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

@@ -0,0 +1,10 @@
+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

@@ -0,0 +1,14 @@
+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>