Single-Case mode

1. Defined
   One-piece mode is to ensure that a class has only one instance and provides a global access point.
2. Case analysis
   Some objects can have only one instance, such as a thread pool, a printer, a graphics card, a registry, and so on. The classic single-piece mode is implemented as follows:

publicclass Singleton{        privatestatic Singleton uniqueInstance;        privateSingleton(){}        publicstaticgetInstance(){            ifnull){                new Singleton();            }            return uniqueInstance;        }}

In multithreaded situations, the getinstance () method can execute two times resulting in two uniqueinstance instances. Just turn the getinstance () into a synchronous (synchronized).

publicclass Singleton{        privatestatic Singleton uniqueInstance;        privateSingleton(){}        publicstatic  getInstance(){            ifnull){                new Singleton();            }            return uniqueInstance;        }}

Single-Case mode