[designmode] singleton pattern

1. Introduction to singleton design patterns

So called class singleton design pattern , Is to take certain methods to ensure that in the whole software system , There can only be one object instance for a class , And this class only provides a method to get its object instance ( Static methods ).

such as Hibernate Of SessionFactory, It acts as a proxy for the datastore source , And responsible for creating Session object .SessionFactory It's not lightweight , In general , A project usually only needs one SessionFactory Is enough , This will be used in singleton mode .

2. There are eight ways to design singleton

There are eight ways of singleton mode ：

1) Hungry Chinese style ( static const )

2) Hungry Chinese style （ Static code block ）

3. Slacker type ( Thread unsafe )

4. Slacker type ( Thread safety , Synchronization method )

5. Slacker type ( Thread safety , Synchronization code block )

6) Double check

7) Static inner class

8) enumeration

3. Hungry Chinese style （ static const ）

Hungry Chinese style （ static const ） Application example

Steps are as follows ： Silicon Valley Java Design patterns

1. Constructor privatization ( prevent new )

2. Create objects inside the class

3. Expose a static public method .getInstance

4. Code implementation