Java's design pattern

Design pattern classification is more, here first to learn a singleton mode

Singleton mode : In a Java application, a singleton object can be guaranteed to exist in one JVM with only one instance of the object . Divided into a hungry man type, Raikhan type, etc.

Our upper and lower code:

1  Packagecom.learn.chap03.sec18;2 3  Public classSingleton1 {4     5     /**6 * Construction method Private 7      */8     PrivateSingleton1 () {9         Ten     } One      A     /** - * A hungry man single-case implementation -      */ the     Private Static Final Singleton1 Single1=NewSingleton1 (); -      -     /** - * Static Factory mode +      */ -      Public Static Singleton1 getinstance (){ +         returnSingle1; A     } at  -}

1  Packagecom.learn.chap03.sec18;2 3  Public classSingleton2 {4     /**5 * Construction method Private 6      */7     PrivateSingleton2 () {8         9     }Ten      One     /** A * Raikhan-type singleton implementation is instantiated at the time of the first call -      */ -     Private Static Singleton2single; the      -     /** - * Factory -      */ +      Public synchronized StaticSingleton2 getinstance () { -         if(single==NULL){ +             //instantiate the first call ASystem.out.println ("Instantiation at first call")); atSingle =NewSingleton2 (); -              -         } -         returnSingle ; -     } -}

1  Packagecom.learn.chap03.sec18;2 3  Public classTestsingleton {4     5      Public Static voidMain (string[] args) {6Singleton1 Singleton1 =singleton1.getinstance ();7Singleton1 Singleton2 =singleton1.getinstance ();8System.out.println ("A Hungry Man Type:" + (Singleton1 = =singleton2));9         TenTestsingleton T1 =NewTestsingleton (); OneTestsingleton t2 =NewTestsingleton (); ASystem.out.println (T1 = =T2)); -          -Singleton2 Singleton3 =singleton2.getinstance (); theSingleton2 Singleton4 =singleton2.getinstance (); -System.out.println ("Lazy Type:" + (Singleton3 = =singleton4)); -          -     } +          -}

Run results

A hungry man type: True
False
Instantiate the first call
Lazy Type: True

Attention:

The difference between the A hungry man and the lazy type is that the A hungry man type is instantiated when initializing a singleton, and the lazy type is instantiated only when the factory initialization method is first called, and no longer instantiated

Java's design pattern