Implementing Singleton with an Enum (in Java)
In the realm of software development, it is not uncommon to encounter scenarios where we need to ensure that a class has only one instance in memory. Singleton, a design pattern, caters to this requirement.
Consider the following Java implementation of Singleton using an enum:
public enum MySingleton { INSTANCE; }
On the surface, one might wonder how this actually works. After all, an object must be instantiated to exist. Here's the breakdown:
Implicit Constructor:
In reality, the enum declaration implicitly calls an empty constructor. However, this is not always clear from the code alone.
Explicit Constructor:
To make things more explicit, we can add a private constructor to the enum:
public enum MySingleton { INSTANCE; private MySingleton() { System.out.println("Here"); } }
Enum Constants and Construction:
Enum fields are essentially compile-time constants, but they are also instances of their enum type. The first time the enum type is referenced, these instances are constructed.
Main Method Demonstration:
If we create a main method in a separate class:
public static void main(String[] args) { System.out.println(MySingleton.INSTANCE); }
We can observe the following output:
Here INSTANCE
In this example, the instance "INSTANCE" is constructed the first time the enum is referenced in the main method.
The above is the detailed content of How Does a Java Enum Implement the Singleton Design Pattern?. For more information, please follow other related articles on the PHP Chinese website!

JVM'sperformanceiscompetitivewithotherruntimes,offeringabalanceofspeed,safety,andproductivity.1)JVMusesJITcompilationfordynamicoptimizations.2)C offersnativeperformancebutlacksJVM'ssafetyfeatures.3)Pythonisslowerbuteasiertouse.4)JavaScript'sJITisles

JavaachievesplatformindependencethroughtheJavaVirtualMachine(JVM),allowingcodetorunonanyplatformwithaJVM.1)Codeiscompiledintobytecode,notmachine-specificcode.2)BytecodeisinterpretedbytheJVM,enablingcross-platformexecution.3)Developersshouldtestacross

TheJVMisanabstractcomputingmachinecrucialforrunningJavaprogramsduetoitsplatform-independentarchitecture.Itincludes:1)ClassLoaderforloadingclasses,2)RuntimeDataAreafordatastorage,3)ExecutionEnginewithInterpreter,JITCompiler,andGarbageCollectorforbytec

JVMhasacloserelationshipwiththeOSasittranslatesJavabytecodeintomachine-specificinstructions,managesmemory,andhandlesgarbagecollection.ThisrelationshipallowsJavatorunonvariousOSenvironments,butitalsopresentschallengeslikedifferentJVMbehaviorsandOS-spe

Java implementation "write once, run everywhere" is compiled into bytecode and run on a Java virtual machine (JVM). 1) Write Java code and compile it into bytecode. 2) Bytecode runs on any platform with JVM installed. 3) Use Java native interface (JNI) to handle platform-specific functions. Despite challenges such as JVM consistency and the use of platform-specific libraries, WORA greatly improves development efficiency and deployment flexibility.

JavaachievesplatformindependencethroughtheJavaVirtualMachine(JVM),allowingcodetorunondifferentoperatingsystemswithoutmodification.TheJVMcompilesJavacodeintoplatform-independentbytecode,whichittheninterpretsandexecutesonthespecificOS,abstractingawayOS

Javaispowerfulduetoitsplatformindependence,object-orientednature,richstandardlibrary,performancecapabilities,andstrongsecurityfeatures.1)PlatformindependenceallowsapplicationstorunonanydevicesupportingJava.2)Object-orientedprogrammingpromotesmodulara

The top Java functions include: 1) object-oriented programming, supporting polymorphism, improving code flexibility and maintainability; 2) exception handling mechanism, improving code robustness through try-catch-finally blocks; 3) garbage collection, simplifying memory management; 4) generics, enhancing type safety; 5) ambda expressions and functional programming to make the code more concise and expressive; 6) rich standard libraries, providing optimized data structures and algorithms.


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

MantisBT
Mantis is an easy-to-deploy web-based defect tracking tool designed to aid in product defect tracking. It requires PHP, MySQL and a web server. Check out our demo and hosting services.

SecLists
SecLists is the ultimate security tester's companion. It is a collection of various types of lists that are frequently used during security assessments, all in one place. SecLists helps make security testing more efficient and productive by conveniently providing all the lists a security tester might need. List types include usernames, passwords, URLs, fuzzing payloads, sensitive data patterns, web shells, and more. The tester can simply pull this repository onto a new test machine and he will have access to every type of list he needs.

SublimeText3 Chinese version
Chinese version, very easy to use

EditPlus Chinese cracked version
Small size, syntax highlighting, does not support code prompt function

Atom editor mac version download
The most popular open source editor
