Java单例模式的实现，包括6种线程安全实现(饿汉式，私有静态内部类式，synchronized方法式，synchronized块式，双重检查式，ThreadLocal式)和1种非线程安全实现(经典懒汉式)。

另外，大家可以参考我的博文《彻头彻尾理解单例模式与多线程》(http://blog.csdn.net/justloveyou_/article/details/64127789)深入了解单例模式的实现与原理。

Author: githubofrico

.classpath

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+<?xml version="1.0" encoding="UTF-8"?>
+<classpath>
+	<classpathentry kind="src" path="src"/>
+	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-1.7"/>
+	<classpathentry kind="output" path="bin"/>
+</classpath>

.gitignore

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+/bin/

.project

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+<?xml version="1.0" encoding="UTF-8"?>
+<projectDescription>
+	<name>SingletonPattern</name>
+	<comment></comment>
+	<projects>
+	</projects>
+	<buildSpec>
+		<buildCommand>
+			<name>org.eclipse.jdt.core.javabuilder</name>
+			<arguments>
+			</arguments>
+		</buildCommand>
+	</buildSpec>
+	<natures>
+		<nature>org.eclipse.jdt.core.javanature</nature>
+	</natures>
+</projectDescription>

.settings/org.eclipse.jdt.core.prefs

@@ -0,0 +1,11 @@
+eclipse.preferences.version=1
+org.eclipse.jdt.core.compiler.codegen.inlineJsrBytecode=enabled
+org.eclipse.jdt.core.compiler.codegen.targetPlatform=1.7
+org.eclipse.jdt.core.compiler.codegen.unusedLocal=preserve
+org.eclipse.jdt.core.compiler.compliance=1.7
+org.eclipse.jdt.core.compiler.debug.lineNumber=generate
+org.eclipse.jdt.core.compiler.debug.localVariable=generate
+org.eclipse.jdt.core.compiler.debug.sourceFile=generate
+org.eclipse.jdt.core.compiler.problem.assertIdentifier=error
+org.eclipse.jdt.core.compiler.problem.enumIdentifier=error
+org.eclipse.jdt.core.compiler.source=1.7

src/p2_singleton_impl_hunger_ThreadSafe_ThreadUnsafe/MultiThreadTest.java

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+package p2_singleton_impl_hunger_ThreadSafe_ThreadUnsafe;
+
+/**        
+ * Title: ¶àÏ̲߳âÊÔ
+ * Description: 
+ * @author rico       
+ * @created 2017Äê5ÔÂ7ÈÕ ÏÂÎç4:41:44    
+ */      
+public class MultiThreadTest {
+	
+	public static void main(String[] args) {
+		
+		MyThread[] threads = new MyThread[20];
+		for (int i = 0; i < threads.length; i++) {
+			threads[i] = new MyThread();
+		}
+		
+		for (int i = 0; i < threads.length; i++) {
+			threads[i].start();
+		}
+	}
+}
+
+class MyThread extends Thread{
+	
+	@Override
+	public void run() {
+		System.out.println(Singleton.getInstance());
+	}
+}

src/p2_singleton_impl_hunger_ThreadSafe_ThreadUnsafe/SingleThreadTest.java

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+package p2_singleton_impl_hunger_ThreadSafe_ThreadUnsafe;
+
+/**        
+ * Title: 单线程测试   
+ * Description: 
+ * @author rico       
+ * @created 2017年5月7日 下午4:42:08    
+ */      
+public class SingleThreadTest {
+	public static void main(String[] args) {
+
+		Singleton instance1 = Singleton.getInstance();
+		
+		Singleton instance2 = Singleton.getInstance();
+		
+		//判断是否是同一个对象
+		System.out.println(instance1 == instance2);
+		
+	}
+}
+

src/p2_singleton_impl_hunger_ThreadSafe_ThreadUnsafe/Singleton.java

@@ -0,0 +1,20 @@
+package p2_singleton_impl_hunger_ThreadSafe_ThreadUnsafe;
+
+/**        
+ * Title: 饿汉式单例模式   
+ * Description: 饿汉式单例模式本身就是线程安全的
+ * @author rico       
+ * @created 2017年5月7日 下午4:22:29    
+ */      
+public class Singleton {
+
+	private static Singleton instance = new Singleton();
+	
+	private Singleton(){
+		
+	}
+	
+	public static Singleton getInstance(){
+		return instance;
+	}
+}

src/p2_singleton_impl_lazy_ThreadSafe_DoubleCheckLock/MultiThreadTest.java

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+package p2_singleton_impl_lazy_ThreadSafe_DoubleCheckLock;
+
+/**        
+ * Title: ¶àÏ̲߳âÊÔ    
+ * Description: 
+ * @author rico       
+ * @created 2017Äê5ÔÂ7ÈÕ ÏÂÎç4:44:10    
+ */      
+public class MultiThreadTest {
+	
+	public static void main(String[] args) {
+		
+		MyThread[] threads = new MyThread[20];
+		for (int i = 0; i < threads.length; i++) {
+			threads[i] = new MyThread();
+		}
+		
+		for (int i = 0; i < threads.length; i++) {
+			threads[i].start();
+		}
+	}
+}
+
+class MyThread extends Thread{
+	
+	@Override
+	public void run() {
+		Singleton instance = Singleton.getInstance();
+		System.out.println(instance);
+	}
+}

src/p2_singleton_impl_lazy_ThreadSafe_DoubleCheckLock/SingleThreadTest.java

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+package p2_singleton_impl_lazy_ThreadSafe_DoubleCheckLock;
+
+  
+/**        
+ * Title: 线程安全的懒汉式单例  
+ * Description: 双重检查锁定
+ * @author rico       
+ * @created 2017年5月7日 下午4:44:57    
+ */      
+public class SingleThreadTest {
+	
+	public static void main(String[] args) {
+
+		Singleton instance1 = Singleton.getInstance();
+		
+		Singleton instance2 = Singleton.getInstance();
+		
+		//判断是否是同一个对象
+		System.out.println(instance1 == instance2);
+		
+	}
+}
+

src/p2_singleton_impl_lazy_ThreadSafe_DoubleCheckLock/Singleton.java

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+package p2_singleton_impl_lazy_ThreadSafe_DoubleCheckLock;
+
+/**
+ * Title: 线程安全的懒汉式单例模式 
+ * Description: 双重检查锁定，效率较高
+ * 
+ * @author rico
+ * @created 2017年5月7日 下午4:22:29
+ */
+public class Singleton {
+
+	// volatile： 防止指令重排序
+	private volatile static Singleton instance;
+
+	private Singleton() {
+
+	}
+
+	public static Singleton getInstance() {
+		// 第一次检查
+		if(instance == null){
+			// 只在最初几次会进入该同步块，提高效率
+			synchronized(Singleton.class){
+				// 第二次检查
+				if(instance == null){
+					instance = new Singleton();
+				}
+			}
+		}
+		return instance;
+	}
+}

src/p2_singleton_impl_lazy_ThreadSafe_InnerClass/MultiThreadTest.java

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+package p2_singleton_impl_lazy_ThreadSafe_InnerClass;
+
+/**        
+ * Title: ¶àÏ̲߳âÊÔ    
+ * Description: 
+ * @author rico       
+ * @created 2017Äê5ÔÂ7ÈÕ ÏÂÎç4:44:10    
+ */      
+public class MultiThreadTest {
+	
+	public static void main(String[] args) {
+		
+		MyThread[] threads = new MyThread[20];
+		for (int i = 0; i < threads.length; i++) {
+			threads[i] = new MyThread();
+		}
+		
+		for (int i = 0; i < threads.length; i++) {
+			threads[i].start();
+		}
+	}
+}
+
+class MyThread extends Thread{
+	
+	@Override
+	public void run() {
+		System.out.println(Singleton.getInstance());
+	}
+}

src/p2_singleton_impl_lazy_ThreadSafe_InnerClass/SingleThreadTest.java

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+package p2_singleton_impl_lazy_ThreadSafe_InnerClass;
+
+  
+/**        
+ * Title: 单线程测试     
+ * Description: 
+ * @author rico       
+ * @created 2017年5月7日 下午4:44:57    
+ */      
+public class SingleThreadTest {
+	
+	public static void main(String[] args) {
+
+		Singleton instance1 = Singleton.getInstance();
+		
+		Singleton instance2 = Singleton.getInstance();
+		
+		//判断是否是同一个对象
+		System.out.println(instance1 == instance2);
+		
+	}
+}
+

src/p2_singleton_impl_lazy_ThreadSafe_InnerClass/Singleton.java

@@ -0,0 +1,23 @@
+package p2_singleton_impl_lazy_ThreadSafe_InnerClass;
+
+/**        
+ * Title: 线程安全的懒汉式单例模式   
+ * Description: 内部类实现
+ * @author rico       
+ * @created 2017年5月7日 下午4:22:29    
+ */      
+public class Singleton {
+
+	//静态私有内部类
+	private static class InnerClass {
+		private final static Singleton instance = new Singleton();
+	}
+	
+	private Singleton(){
+		
+	}
+	
+	public static Singleton getInstance(){
+		return InnerClass.instance;
+	}
+}

src/p2_singleton_impl_lazy_ThreadSafe_Synchronized/MultiThreadTest.java

@@ -0,0 +1,31 @@
+package p2_singleton_impl_lazy_ThreadSafe_Synchronized;
+
+/**        
+ * Title: ¶àÏ̲߳âÊÔ    
+ * Description: 
+ * @author rico       
+ * @created 2017Äê5ÔÂ7ÈÕ ÏÂÎç4:44:10    
+ */      
+public class MultiThreadTest {
+	
+	public static void main(String[] args) {
+		
+		MyThread[] threads = new MyThread[20];
+		for (int i = 0; i < threads.length; i++) {
+			threads[i] = new MyThread();
+		}
+		
+		for (int i = 0; i < threads.length; i++) {
+			threads[i].start();
+		}
+	}
+}
+
+class MyThread extends Thread{
+	
+	@Override
+	public void run() {
+		Singleton instance = Singleton.getInstance();
+		System.out.println(instance);
+	}
+}

src/p2_singleton_impl_lazy_ThreadSafe_Synchronized/SingleThreadTest.java

@@ -0,0 +1,23 @@
+package p2_singleton_impl_lazy_ThreadSafe_Synchronized;
+
+  
+/**        
+ * Title: 单线程测试     
+ * Description: 
+ * @author rico       
+ * @created 2017年5月7日 下午4:44:57    
+ */      
+public class SingleThreadTest {
+	
+	public static void main(String[] args) {
+
+		Singleton instance1 = Singleton.getInstance();
+		
+		Singleton instance2 = Singleton.getInstance();
+		
+		//判断是否是同一个对象
+		System.out.println(instance1 == instance2);
+		
+	}
+}
+

src/p2_singleton_impl_lazy_ThreadSafe_Synchronized/Singleton.java

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+package p2_singleton_impl_lazy_ThreadSafe_Synchronized;
+
+/**
+ * Title: 线程安全的懒汉式单例模式 
+ * Description: 同步方法实现，相比双重检查锁定，效率较低
+ * 
+ * @author rico
+ * @created 2017年5月7日 下午4:22:29
+ */
+public class Singleton {
+
+	private static Singleton instance;
+
+	private Singleton() {
+
+	}
+
+	// 同步方法
+	public synchronized static Singleton getInstance() {
+		if(instance == null){
+			instance = new Singleton();
+		}
+		return instance;
+	}
+}

src/p2_singleton_impl_lazy_ThreadSafe_SynchronizedBlock/MultiThreadTest.java

@@ -0,0 +1,31 @@
+package p2_singleton_impl_lazy_ThreadSafe_SynchronizedBlock;
+
+/**        
+ * Title: ¶àÏ̲߳âÊÔ    
+ * Description: 
+ * @author rico       
+ * @created 2017Äê5ÔÂ7ÈÕ ÏÂÎç4:44:10    
+ */      
+public class MultiThreadTest {
+	
+	public static void main(String[] args) {
+		
+		MyThread[] threads = new MyThread[20];
+		for (int i = 0; i < threads.length; i++) {
+			threads[i] = new MyThread();
+		}
+		
+		for (int i = 0; i < threads.length; i++) {
+			threads[i].start();
+		}
+	}
+}
+
+class MyThread extends Thread{
+	
+	@Override
+	public void run() {
+		Singleton instance = Singleton.getInstance();
+		System.out.println(instance);
+	}
+}