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In this article, the editor introduces "what are the web design patterns" in detail, the content is detailed, the steps are clear, and the details are handled properly. I hope this article "what are the web design patterns" can help you solve your doubts? let's follow the editor's ideas to learn new knowledge.

123 design modes:

Creative pattern:-singleton pattern, factory pattern, abstract factory pattern, builder pattern, prototype pattern.

Structural mode:-adapter mode, bridge mode, decoration mode, combination mode, appearance mode, sharing meta mode, style.

Behavioral pattern:-template method mode, command mode, iterator mode, observer mode, intermediary mode, standby mode, interpreter mode, state mode, policy mode, responsibility chain mode, visitor

In fact, these design patterns are just an idea, we do not need to memorize all the code, but the designer's thinking into everyone's study and work, a higher level of thinking!

2 singleton mode

Singleton mode is mainly divided into two types, the other types we do not explain: hungry Han style (thread safety, high call efficiency. However, you cannot delay loading. )

Lazy (thread-safe, inefficient call. However, you can delay loading

So what is the use of a single case?

Core role:-ensure that there is only one instance of a class and provide a global access to that instance

Let me give you some very common examples.

Windows's Task Manager (Task Manager) is a typical singleton mode.

Windows's Recycle Bin (Recycle Bin) is also a typical singleton application. Throughout the operation of the system, the Recycle Bin maintains the only one.

What are the advantages:

-because the singleton mode generates only one instance, which reduces the system performance overhead, when the generation of an object requires more resources, such as reading configuration and generating other dependent objects, it can be solved by directly generating a singleton object at the start of the application and then permanently residing in memory.

The singleton mode can set global access points in the system and optimize ring shared resource access. For example, a singleton class can be designed to map all data tables.

(3) single case of hungry Han style

Public class SingletonDemo1 {

The object is loaded immediately when the class is initialized (there is no advantage of delayed loading). When loading classes, it is naturally thread-safe!

Private static SingletonDemo1 instance = new SingletonDemo1 ()

Private SingletonDemo1 () {

}

/ / the method is not synchronized, and the call efficiency is high!

Public static SingletonDemo1 getInstance () {

Return instance

}

}

Hungry Chinese style, as the name implies, one word-hungry, must be that as soon as the class is loaded, an object will be new (the static variable will be initialized when the class is loaded). At this time, multiple thread objects will not be involved in accessing the object. The virtual machine is guaranteed to load this class only once, and the problem of concurrent access will certainly not occur. Therefore, the synchronized key can be omitted.

But there is a problem: when we use this object or not, it will help us new this object, which will lead to a waste of resources!

4 single case of lazy man style

Public class SingletonDemo2 {

The object is not initialized when the class is initialized (delayed loading and created when it is actually used).

Private static SingletonDemo2 instance

Private SingletonDemo2 () {/ / privatized constructor

}

/ / the method is synchronized, and the calling efficiency is low!

Public static synchronized SingletonDemo2 getInstance () {

If (instance==null) {

Instance = new SingletonDemo2 ()

}

Return instance

}

}

Lazy style, as the name implies, a word-lazy, that is, when we need him, we new him out, and we don't new it when we don't need it.

But there will also be some problems: the utilization of resources is high. However, the getInstance () method should be synchronized every time it is called, and it is more efficient to send it concurrently.

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