Detailed explanation of single example mode of Android design mode

Singleton mode

A class has only one instance and can be accessed and used globally

Application scenario

Such as account management class, database operation class, etc. (an object is frequently accessed and used)

Common way

Hungry lazy synchronous locking DCL double locking verification static internal class enumeration singleton

Initialization is performed immediately while loading classes, which consumes a lot of resources

Lazy style

Advantages: initialization loading is performed only when it needs to be used

Disadvantages: threads are unsafe, and it is easy to be out of sync in multithreading

Synchronous locking

Advantages: solve thread safety problems

Disadvantages: each instance needs to judge the locking state, which is inefficient

DCL double check

Advantages: it can run perfectly when the concurrency is not high (recommended, there is almost no high concurrency on the client)

Disadvantages: before JDK 1.5, the instance initialization problem may occur (now Android is almost 1.7 and 1.8, which can be ignored)

Static inner class

Advantages: delayed loading, thread safety, less memory consumption (recommended)

Enumeration singleton

Advantages: thread safety, anti deserialization, anti reflection, simple writing

GitHub code address

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