Core role:
– Ensures that a class has only one instance and provides a global access point to that instance
The computer manager, once created a task manager, to create the same again.
1. Singleton mode: Hangry.
Hungry: The same object no matter how many objects are created
Two, lazy: with delayed loading. Add synchronization, call efficiency is low.
Double check locks: Occasionally problems occur due to compiler optimizations and JVM underlying internal models
Not recommended.
Four: static inner class pattern
Advantages: 1 thread safety, 2 call efficiency, 3 lazy loading
/** * The external class has no static property, so it does not load the object immediately. ** * The external class has no static property, so it does not load the object immediately. ** * The external class has no static property, so it does not load the object immediately. And can only be assigned once, thus ensuring thread safety * with the advantages of concurrent efficient calls and slow loading. * * /
Enumerative singleton pattern
The enumeration element itself is a singleton, thread-safe,
Natural protection against reflection and deserialization vulnerabilities
But there is no delayed loading
Test time:
