Shulou(Shulou.com)06/03 Report--

Today, I will talk to you about what the singleton class of jad enumeration in java is like. Many people may not know much about it. In order to make you understand better, the editor has summarized the following content for you. I hope you can get something according to this article.

First, take a look at the singleton class that enumerates the implementation

Ordinary class

Public class Controller {public Controller () {} public void func () {System.out.println ("1");}}

I want to make it singleton (use an enumerated class to hold the normal class that you want to implement the singleton)

Public enum ControllerHolder {INSTANCE; private Controller controller; ControllerHolder () {this.controller = new Controller ();} public static Controller getInstance () {return ControllerHolder.INSTANCE.controller;}}

Test it.

Public static void main (String [] args) {System.out.println (ControllerHolder.getInstance ()); System.out.println (ControllerHolder.getInstance ()); System.out.println (ControllerHolder.getInstance ()); System.out.println (ControllerHolder.getInstance ()); System.out.println (ControllerHolder.getInstance ()) } output: com.iluwatar.singleton.Controller@6e8cf4c6com.iluwatar.singleton.Controller@6e8cf4c6com.iluwatar.singleton.Controller@6e8cf4c6com.iluwatar.singleton.Controller@6e8cf4c6com.iluwatar.singleton.Controller@6e8cf4c6

Now it looks like a singleton, but does it support multithreading? Decompiler, take a look.

Under the source code directory, execute javac. / *. Java to compile all the files under the package

Use the javap decompilation that comes with java to see javap.\ ControllerHolder.class

The decompilation of javap is not very good. I can't see the specific situation. Let's use jad to decompile.

Execute.\ jad.exe D:\ workspace_idea_try\ java-design-patterns\ singleton\ src\ main\ java\ com\ zzk\ singleton\ ControllerHolder.class will generate a ControllerHolder.jad file in the jad.exe sibling directory. The contents are as follows: ↓↓↓

The last decompiled file

Public final class ControllerHolder extends Enum {public static ControllerHolder [] values () {return (ControllerHolder []) $VALUES.clone ();} public static ControllerHolder valueOf (String s) {return (ControllerHolder) Enum.valueOf (com/zzk/singleton/ControllerHolder, s);} private ControllerHolder (String s, int I) {super (s, I); controller = new Controller () } public static Controller getInstance () {return INSTANCE.controller;} public static final ControllerHolder INSTANCE; / / controller initializes private Controller controller; private static final ControllerHolder $VALUES [] with ControllerHolder initialization; static {INSTANCE = new ControllerHolder ("INSTANCE", 0); $VALUES = (new ControllerHolder [] {INSTANCE});}}

The public final class ControllerHolder extends Enum line shows that enumeration is a normal class that only inherits the Enum class.

In the public static final ControllerHolder INSTANCE; line, ControllerHolder is static and INSTANCE = new ControllerHolder ("INSTANCE", 0); executed in a static code block, jvm ensures that running static code blocks are thread-safe and executed only once, so Controller, as an attribute of ControllerHolder, is naturally declared only once and thread-safe.

The implementation of this enumeration singleton does not have the advantage of delayed loading and is initialized in static methods.

As written above, Controller and ControllerHolder are written separately, which is generally not used, because if someone directly new a Controller, it will cause the Controller to be not a singleton, so the usual way to write the enumeration is to write the enumeration as an internal enumeration class, the code is as follows:

Public class SingletonExample7 {/ / Private constructor private SingletonExample7 () {} public static SingletonExample7 getInstance () {return Singleton.INSTANCE.getInstance ();} private enum Singleton {INSTANCE; private SingletonExample7 singleton; / / JVM guarantees that this method will only call Singleton () {singleton = new SingletonExample7 () once absolutely. } public SingletonExample7 getInstance () {return singleton;} after reading the above, do you have any further understanding of the singleton class implemented by the jad enumeration in java? If you want to know more knowledge or related content, please follow the industry information channel, thank you for your support.

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