1 /** 2  * 单例模式:保证只有一个实例 private Singleton(){}; 3  * 饿汉式:先创建 private static final Singleton INSTANCE = new Singleton(); 用的时候调用 public static Singleton getInstance(){return INSTANCE;} 4  * 懒汉式:用的时候创建实例。 5  *         synchronized在方法内,则主要double-check; 6  *         同步在方法上 public static synchronized Singleton getInstance(){ if(instanceLazy==null) instanceLazy=new Singleton();return instanceLazy;} 7  * 静态代码块: 8  *         static{ instanceStaticBlock = new Singleton();} 9  * 静态内部类:10  *         private static class SingletonHolder{ public static final INSTANCE_STATIC_CLASS=new Singleton();}11  * 枚举:12  *         public enum SingletonEnum{INSTANCE;}13  */14 public class Singleton implements Serializable{15     private Singleton(){};  // 私有化构造方法,外部无法创建本类 16     // 饿汉式17     private static final Singleton INSTANCE = new Singleton();18     public static Singleton getInstanceEager(){ return INSTANCE; }19     // 懒汉式20     private static volatile Singleton instanceLazy = null;21     public static Singleton getInstanceLazy1(){22         if(instanceLazy == null){23             synchronized(Singleton.class){24                 if(instanceLazy == null){25                     instanceLazy = new Singleton();26                 }27             }28         }29         return instanceLazy;30     }31     public static synchronized Singleton getInstanceLazy2(){32         if(instanceLazy == null){33             instanceLazy = new Singleton();34         }35         return instanceLazy;36     }37     // 静态代码块38     private static Singleton instanceStaticBlock = null;39     static{40         instanceStaticBlock = new Singleton();41     }42     public static Singleton getInstanceStaticBlock(){ return instanceStaticBlock; }43     // 静态内部类44     private static class SingletonHolder{ public static final Singleton INSTANCE = new Singleton(); }45     public static Singleton getInstanceStaticClass(){ return SingletonHolder.INSTANCE; }46     47     // 砖家建议:功能完善,性能更佳,不存在序列化等问题的单例 就是 静态内部类 + 如下的代码48     private static final long serialVersionUID = 1L;49     protected Object readResolve(){ return getInstanceStaticClass(); }50 }51 //枚举52 enum SingletonEnum{53     INSTANCE;54 }