单例模式：饿汉式、懒汉式；线程安全的单例模式创建的6种方式

单例模式

单�index.php/tags-41973.html" >��模式Singleton是一种创建型模式，指某个采用Singleton单例模式，则这个类在同一个

JVM上，只能产生一个实例供外部访问，并且仅提供一个全局的访问方式。

懒汉式

懒汉式线程不安全

public class Singleton1 {private static Singleton1 instance;// 构造方法私有化！！！private Singleton1() {};public static Singleton1 getInstance() {if(instance == null) {instance = new Singleton1();}return instance;}}

饿汉式

饿汉式线程安全

public class Singleton2 {private static final Singleton2 instance = new Singleton2();// 构造方法私有化private Singleton2() {};public static Singleton2 getInstance() {return instance;}}

线程安全的单例模式

1. 饿汉式线程安全
2. 全局锁线程安全
3. 静态代码块创建单例对象线程安全
4. 双重校验锁实现线程安全
5. 静态内部类实现线程安全的单例模式
6. 内部枚举类实现线程安全

• 全局锁

  public class Singleton3 {private static Singleton3 instance;// 构造方法私有化private Singleton3() {};// 通过synchronized添加全局锁实现线程安全public static synchronized Singleton3 getInstance() {if (instance == null) {instance = new Singleton3();}return instance;}}

• 静态代码块

  public class Singleton4 {private static final Singleton4 instance;// 静态代码块创建单例对象static {instance = new Singleton4();}// 构造方法私有化private Singleton4(){}  public static Singleton4 getInstance() {return instance;}}

• 双重校验锁

  public class Singleton5 {private static Singleton5 instance;private Singleton5() {}public static Singleton5 getInstance() {if (instance == null) {synchronized (Singleton5.class) {if (instance == null) {instance = new Singleton5();}}}return instance;}}

• 静态内部类

  public class Singleton6 {// 构造方法私有化private Singleton6() {};// 静态内部类private static class SingletonHolder{// 创建单例对象private static Singleton6 instance = new Singleton6();}public static Singleton6 getInstance() {return Singleton6.SingletonHolder.instance;}}

• 静态枚举类

  public class Singleton7 {private Singleton7() {}// 内部枚举类enum SingletonEnum{INSTANCE;// 单例对象private Singleton7 instance;    private SingletonEnum() {instance = new Singleton7();}    private static Singleton7 getInstance() {return SingletonEnum.INSTANCE.instance;}}}