What is the singleton pattern?
The singleton pattern is a common design pattern that ensures that instances of a class are singletons.
Advantages of singleton mode:
(1) First of all, it must save memory resources. No matter how frequently instances are created through exposed methods, they can be guaranteed to be created. The object is the same instance object in the system memory;
(2) Flexibility, since the creation of all instances is controlled by this class, all this class can flexibly change the instantiation process;
(3) Controlled access to instances. Singleton classes can easily control controlled access to unique instances;
Disadvantages of singleton mode:
(1) The singleton mode has no interface and is not easy to extend;
(2) You cannot use reflection mode to create a singleton, otherwise a new object will be instantiated;
(3) Use lazy singleton Pay attention to thread safety issues when using the example mode;
Ways to implement the singleton mode:
Singleton method
package index;
public class Superman {
//空的構(gòu)造器
private Superman(){}
//實(shí)例化對(duì)象
private static Superman supermanInstance = new Superman();
//獲取實(shí)例化對(duì)象的靜態(tài)函數(shù)getSupermanInstance()
public static Superman getSupermanInstance(){
return supermanInstance;
}
}The singleton is new in advance when the class is loaded, and a supermanInstance object is instantiated at the beginning. Whether your program needs to call this object or not, it is already ready; there is no delay. Loading, in order to reduce the program load, lazy loading is required in most cases, so this way of implementing a singleton is not the best choice.
Lazy singleton method (single-threaded writing)
package index;
public class Superman {
//空的構(gòu)造器
private Superman(){}
//實(shí)例化對(duì)象;只聲明 不使用new進(jìn)行實(shí)例化
private static Superman supermanInstance = null;
//獲取實(shí)例化對(duì)象的靜態(tài)函數(shù)getSupermanInstance()
public static Superman getSupermanInstance(){
if(supermanInstance==null){ //如果為null的情況再進(jìn)行實(shí)例化
supermanInstance = new Superman();
}
return supermanInstance;
}
}Declare an object without instantiating it, and call the static factory when the program needs to instantiate it. Method getSupermanInstance(), the declared object is judged in the method, and if it is null, instantiate it. This writing method can achieve the effect of delayed loading, but it is not thread-safe. If there are two threads in multi-threading At the same time, calling the static factory method getSupermanInstance() may repeatedly create instances of this class, destroying the uniqueness of the singleton;
Recommended tutorial: Java tutorial
The above is the detailed content of what is java singleton pattern. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undress AI Tool
Undress images for free
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
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
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
VSCode settings.json location
Aug 01, 2025 am 06:12 AM
The settings.json file is located in the user-level or workspace-level path and is used to customize VSCode settings. 1. User-level path: Windows is C:\Users\\AppData\Roaming\Code\User\settings.json, macOS is /Users//Library/ApplicationSupport/Code/User/settings.json, Linux is /home//.config/Code/User/settings.json; 2. Workspace-level path: .vscode/settings in the project root directory
How to handle transactions in Java with JDBC?
Aug 02, 2025 pm 12:29 PM
To correctly handle JDBC transactions, you must first turn off the automatic commit mode, then perform multiple operations, and finally commit or rollback according to the results; 1. Call conn.setAutoCommit(false) to start the transaction; 2. Execute multiple SQL operations, such as INSERT and UPDATE; 3. Call conn.commit() if all operations are successful, and call conn.rollback() if an exception occurs to ensure data consistency; at the same time, try-with-resources should be used to manage resources, properly handle exceptions and close connections to avoid connection leakage; in addition, it is recommended to use connection pools and set save points to achieve partial rollback, and keep transactions as short as possible to improve performance.
Mastering Dependency Injection in Java with Spring and Guice
Aug 01, 2025 am 05:53 AM
DependencyInjection(DI)isadesignpatternwhereobjectsreceivedependenciesexternally,promotingloosecouplingandeasiertestingthroughconstructor,setter,orfieldinjection.2.SpringFrameworkusesannotationslike@Component,@Service,and@AutowiredwithJava-basedconfi
How to work with Calendar in Java?
Aug 02, 2025 am 02:38 AM
Use classes in the java.time package to replace the old Date and Calendar classes; 2. Get the current date and time through LocalDate, LocalDateTime and LocalTime; 3. Create a specific date and time using the of() method; 4. Use the plus/minus method to immutably increase and decrease the time; 5. Use ZonedDateTime and ZoneId to process the time zone; 6. Format and parse date strings through DateTimeFormatter; 7. Use Instant to be compatible with the old date types when necessary; date processing in modern Java should give priority to using java.timeAPI, which provides clear, immutable and linear
Understanding the Java Virtual Machine (JVM) Internals
Aug 01, 2025 am 06:31 AM
TheJVMenablesJava’s"writeonce,runanywhere"capabilitybyexecutingbytecodethroughfourmaincomponents:1.TheClassLoaderSubsystemloads,links,andinitializes.classfilesusingbootstrap,extension,andapplicationclassloaders,ensuringsecureandlazyclassloa
Google Chrome cannot open local files
Aug 01, 2025 am 05:24 AM
ChromecanopenlocalfileslikeHTMLandPDFsbyusing"Openfile"ordraggingthemintothebrowser;ensuretheaddressstartswithfile:///;2.SecurityrestrictionsblockAJAX,localStorage,andcross-folderaccessonfile://;usealocalserverlikepython-mhttp.server8000tor
Comparing Java Frameworks: Spring Boot vs Quarkus vs Micronaut
Aug 04, 2025 pm 12:48 PM
Pre-formanceTartuptimeMoryusage, Quarkusandmicronautleadduetocompile-Timeprocessingandgraalvsupport, Withquarkusoftenperforminglightbetterine ServerLess scenarios.2.Thyvelopecosyste,
Understanding Network Ports and Firewalls
Aug 01, 2025 am 06:40 AM
Networkportsandfirewallsworktogethertoenablecommunicationwhileensuringsecurity.1.Networkportsarevirtualendpointsnumbered0–65535,withwell-knownportslike80(HTTP),443(HTTPS),22(SSH),and25(SMTP)identifyingspecificservices.2.PortsoperateoverTCP(reliable,c
