Design Pattern series-singleton

I. Class Diagram

 

Ii. Intention

Ensure that a class has only one instance and provides a global access point to it.

Iii. Applicability

A) when the class can only have one instance and the customer can access it from a well-known access point.

B) when this unique instance should be extensible through subclass, and the customer should not need to changeCodeYou can use an extended instance.

IV. Implementation Method

1. Lazy Mode

 Package Effece. Singleton;

 //  Lazy Mode
  //  It is not initialized until the first call.  
  Public  Class Singleton1 {
 Private   Static Singleton1 instance = Null ;

 Private Singleton1 (){
}

 Public   Static   Synchronized Singleton1 getinstance (){
 If (Instance = Null ){
Instance =New Singleton1 ();
}
 Return Instance;
}
}

2. Hunger Mode

PackageEffece. Singleton;
//Hunger mode,
//Initial Plan upon declaration
Public ClassSingleton2 {
Private StaticSingleton2 instace =NewSingleton2 ();

PrivateSingleton2 (){
}

Public StaticSingleton2 getinstance (){
ReturnInstace;
}
}
 

3. Double Check Mode

 Package Effece. Singleton;
//  Double Check Mode
  //  Not secure:  Http://www.ibm.com/developerworks/cn/java/j-dcl.html  
  Public   Class Singleton3 {
 Private   Static   Volatile Singleton3 instance = Null ;

 Private Singleton3 (){}

 Public   Static Singleton3 getinstance (){
 If (Instance = Null ){
 Synchronized (Singleton3. Class ){
 If (Instance = Null ){
Instance = New Singleton3 ();
}
}
}
 Return Instance;
}
}

5. RuntimeClass Singleton Mode

 
Public ClassRuntime {
Private StaticRuntime currentruntime =NewRuntime ();

Public StaticRuntime getruntime (){
ReturnCurrentruntime;
}
 

Not explained: clear at a glance.