one note of Head first design patterns(singleton pattern)

I read the singleto pattern with the  head first  design pattern yestarday evening.i will review it .

      First of all ,we should konw about the offical definition of the pattern,here is it .the singleto

ensures that a class has only one instance, and provide a global point of access to it .it  is used

to treat with the following  situation.when we just need one instance of a class,what's more.the

object needs to be accessed at a global level.there are two forms about this pattern as follows:

java 代码

public class Singleto {

     private static Singleto instance  ;

     private Singleto(){ }

     public static synchronized Singleto getInstance(){

           if(instance==null){

                instance = new Singleto();
           }else
                return instance ;
     }


}
//the synchroinzed key ensure the only one instance at the mutilthread access.

 

java 代码

public class Singleto {

     private static Singleto instance = new Singleto() ;

     private Singleto(){ }

     public static Singleto getInstance(){

              return instance ;
     }


}