My views on Singleton mode and my views on Mode

My views on Singleton mode and my views on Mode

The Singleton mode is the most common design mode. If you want to enter a large company, you must thoroughly master the singleton mode and summarize some common Singleton modes.

First of all, it is the most simple cool-man mode. The cool-man mode is the simplest Singleton mode.

/*** Invalid mode */public class SingleTon {private static final SingleTon instance = new SingleTon (); private SingleTon () {} public static SingleTon getInstance () {return instance ;}}

It is actually the lazy loading mode. The simplest lazy loading mode is as follows:

public class SingleTon {private static SingleTon instance = null ;private SingleTon(){}public  static SingleTon getInstance() {if (instance == null) {instance = new SingleTon();}return instance;}}

However, the preceding lazy mode is thread insecure and can be locked.

public class SingleTon {private static SingleTon instance = null ;private SingleTon(){}public static synchronized SingleTon getInstace(){if (instances == null ) {return instances = new SingleTon();}return instances;}}

Or double lock mode

public class SingleTon {private static SingleTon instance = null ;private SingleTon(){}public static SingleTon getInstance(){if (instances == null) {synchronized (SingleTon.class) {instances = new SingleTon();}}return instances;}}

　　

The Singleton mode can also be implemented using internal classes.

      public class SingleTon {      public static class SingleTonHolder{private static SingleTon instance = new SingleTon();}public SingleTon() {}public static SingleTon getInstance() {return SingleTonHolder.instance;}}    

Let's see how Daniel Jon Skeet writes a singleton (c)

public sealed class Singleton{    Singleton()    {    }    public static Singleton Instance    {        get        {            return Nested.instance;        }    }    class Nested    {        // Explicit static constructor to tell C# compiler        // not to mark type as beforefieldinit        static Nested()        {        }        internal static readonly Singleton instance = new Singleton();    }}

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What is Singleton mode?

Hello, you can start with a question: how can I instantiate a class only once in java?
The answer is: Singleton mode.

The code is embodied in
Public class {
Private A () {}// set the constructor to private, and other classes cannot be called for instantiation.
Private static A instance = new A (); // the only instance with the static attribute added.
Public static A getInstance () {// the only entry for other classes to call A, which is also A static attribute. The call method is A. getInstance ()
Return instance;
}
}

Singleton Mode

Only new instances can be created.
Your getInstance method only returns the reference of the EagerSingleton object and does not use new. Of course it is a singleton.