Java implements various types of singleton patterns

Single example is the simplest design mode, the use of self-needless to say, but write a simple case is also a test of a procedural ape foundation, which is why many interviewers are happy to let the interviewer write a single case, is so-called simple and not simple. Needless to say, the following Java to implement a variety of single-case bar.
1. A Hungry man mode

publicclass Singleton{  privatestaticnew Singleton();  privateSingleton(){}  publicstaticgetInstance(){    return instance;  }}

2. Lazy mode

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

3. Thread-Safe single-case mode

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

4. Double-checked thread-safe single-case mode

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

5. The best thread-safe notation

publicclass Singleton{  privateSingleton(){}  privateclass SingletonHolder{    privatestaticnew Singleton();    publicstaticgetInstance(){      return instance;    }  }  publicstaticgetInstance(){    return SingletonHolder.getInstance();  }}

Java implements various types of singleton patterns