Creation Mode (5): Singleton (Singleton Mode)

Singleton mode ensures that a class has only one instance, and the instance Singleton mode is self-instantiated and provided to the entire system. The Singleton mode can only be used when there is a real "Single Instance" demand.

 1   Class Singleton {
 2       Private   Static Singleton sing;
 3  
 4       Private Singleton (){
 5 }
 6  
 7       Public  Static Singleton getinstance (){
 8           If (Sing = Null ){
 9 Sing = New Singleton ();
 10 }
 11           Return Sing;
 12 }
 13 }
14  
 15   Public   Class Test {
 16       Public   Static   Void Main (string [] ARGs ){
 17 Singleton sing = singleton. getinstance ();
 18 Singleton sing2 = singleton. getinstance ();
 19 System. Out. println (SING );
20 System. Out. println (sing2 );
 21 }
 22 }

However, this Singleton mode seems to have some problems. In the case of multi-thread concurrency, there may still be two Singleton cases in the IF (sing = NULL) judgment, to avoid this, you 'd better change it:

1 ClassSingleton {
2PrivateSingleton (){}
3Private StaticSingleton sing =NewSingleton ();
4Public StaticSingleton getinstance (){
5ReturnSing;
6}
7}
 

There is also a singleton ~

Use enumeration:

EnumSingleton {
Sing;
//Method
Public VoidTest (){
System. Out. println ("Singleton ");
}
}
 

Because each enumeration is a singleton by default

 

Thought it was over? No ~ Use static internal classes:

ClassSingleton {
Private Static ClassSingletoninner {
Private StaticSingleton sing =NewSingleton ();
}
PrivateSingleton (){}
Public StaticSingleton getinstance (){
ReturnSingletoninner. Sing;
}
}
 

The advantage of this is that you can call the internal class to create this Singleton only when the class is not created during loading.