java - Singleton Implementation example -

i trying find own way of java singleton implementation. code follows:

public class singleton{    private volatile static singleton _instance = null;    private singleton(){}    public static singleton getinstance(){       if (_instance == null)          object obj = new object();          synchronized(obj){             if (_instance == null)                _instance = new singleton();          }       return _instance; } 

does code work? if not work, how fix it?

no, it's not correct, should synchronize on singleton.class

class singleton {        private volatile static singleton _instance;        private singleton(){}        public static singleton getinstance(){           if (_instance == null)              synchronized(singleton.class){                 if (_instance == null)                    _instance = new singleton();              }           return _instance;     } } 

it's known double-checked locking pattern, see http://www.ibm.com/developerworks/java/library/j-dcl/index.html details

note since there's 1 method in class following serves same purpose without double-checked tricks , it's lazy too

class singleton {        private static singleton _instance = new singleton();        private singleton(){}        public static singleton getinstance(){           return _instance;     } }