Java Singleton mode

Singleton mode ensures that only one instance of a class exists.

In a computer system, the driver objects of the thread pool, cache, log Object, dialog box, printer, and video card are often designed as singleton.

A hungry man method

publicclassSingleton {  

     private static Singleton = new Singleton();      private Singleton() {}      public static getSignleton(){          return singleton;      } }A hungry man in the creation of a class at the same time has created a static object for the system to use, no longer change, so it is inherently thread-safe. However, you cannot defer creating objects. Lazy Type public class Singleton {      private static Singleton singleton = null ;      private Singleton(){}      public static Singleton getSingleton() {          if (singleton == null ) singleton = new Singleton();          return singleton;      } }Lazy Singleton class. Instantiate yourself at the first call, without regard to thread safety, which is thread insecure public class Singleton {          private Singleton(){}               public static Singleton getSingleton(){          return Holder.singleton;      }       private static class Holder {          private static Singleton singleton =  new Singleton();      } } through static internal classes, delayed loading, and thread-safe (this avoids the creation of static instances when the Singleton class is loaded, and because static inner classes are only loaded once, this is also thread-safe:) Enumeration Notation

 Public enum enumsingleton{
INSTANCE;

}
Access via Enumsingleton test=enumsingleton.instance

The use of enumerations, in addition to thread-safe and anti-reflection forced invocation of the constructor, also provides an automatic serialization mechanism to prevent deserialization when a new object is created. Therefore, effective Java recommends using enumerations as much as possible to implement the singleton.

Java Singleton mode