Home Java javaTutorial A brief analysis of the singleton pattern and simple factory pattern in Java design pattern programming

A brief analysis of the singleton pattern and simple factory pattern in Java design pattern programming

Dec 15, 2016 pm 02:35 PM

Singleton Pattern
Motivation
Sometimes it is important to have only one instance of a class. For example, a system should have only one instance of window management.

The singleton pattern is the simplest design pattern: a class is responsible for instantiating itself, ensuring that there is only one instance, and providing an entrance to access this instance.

Purpose
1. Ensure that only one instance is created.
2. Provide access to this instance.

A brief analysis of the singleton pattern and simple factory pattern in Java design pattern programming

Use final to ensure it is created once, and private constructor to ensure not to be instantiated. The public getInstance method ensures external access. The following is the hungry mode:

public class Singleton {
  private static final Singleton instance = new Singleton();
   
  private Singleton() {}
   
  public static Singleton getInstance() {
    return instance;
  }
}
Copy after login


The lazy mode:

public class SingletonDemo {
    private static volatile SingletonDemo instance = null;
   
    private SingletonDemo() {    }
   
    public static SingletonDemo getInstance() {
        if (instance == null) {
            synchronized (SingletonDemo .class){
                if (instance == null) {
                    instance = new SingletonDemo ();
                }
           }
        }
        return instance;
    }
}
Copy after login


Applicable scenarios and examples
1. Logger class, which prevents a Logger instance from being created every time the log is printed.
2. Control class, generally there is only one control instance in the entire system.

Specific issues and implementation
1. Thread safety, a robust singleton pattern should be thread safe.
2. Lazy mode uses a double lock mechanism.
3. Hungry mode uses static variables, which are instantiated when the program is loaded, ensuring that there is only one instance.
4. Abstract factories and factory methods are usually designed in singleton mode to ensure that there is only one factory.
5. When using serialization and deserialization, multiple instances will be created. Use the readResolve function to avoid this situation, but it is best not to use serialization.

   public class Singleton implements Serializable {
...
  
// This method is called immediately after an object of this class is deserialized.
// This method returns the singleton instance.
protected Object readResolve() {
  return getInstance();
}
}
Copy after login


Key points
1. In multi-threaded programs, pay attention to data synchronization.
2. Use the readResolve method to return an instance when serializing to avoid multiple objects being created.
3. If loaded by multiple class loaders, multiple instances will be created.


Simple Factory Pattern
Motivation
Simple Factory Pattern is the basis and preliminary implementation of abstract factory and factory method.

Purpose
1. Do not disclose object instantiation details to clients.
2. Create objects through common interfaces.

Implementation

A brief analysis of the singleton pattern and simple factory pattern in Java design pattern programming

The implementation is very simple:
1. When the Client needs a Product, it does not use new to create it, but provides the Product description to the Factory and lets the Factory provide a new Product.
2. Factory instantiates a Product to the Client.
3. Client uses abstract Product and does not care about the specific implementation of Product.

Example
1. Drawing program for drawing shapes. The shape is the Product interface, and the triangle is the Concrete Product. We can create a factory and then create the corresponding product according to the customer's description. But when adding new shapes, we need to modify the factory class.

Specific issues and implementation
1. When adding new products, the factory needs to be modified.

public class ProductFactory{
  public Product createProduct(String ProductID){
    if (id==ID1)
      return new OneProduct();
    if (id==ID2) 
      return new AnotherProduct();
    ... // so on for the other Ids
      
    return null; //if the id doesn't have any of the expected values
  }
  ...
}
Copy after login

Generally we judge product descriptions through if statements and instantiate different products. When there are new products, we need to add new judgments. This problem can be solved through the abstract factory pattern.

Summary
1. Use the factory pattern only when you really need it, otherwise it will only increase the complexity of the program. For example, when multiple objects have similar basic types, you can consider using the simple factory pattern to create objects uniformly.
2. Simple factory has a lot of judgment branch statements, which violates the open-close principle of closing modifications. Therefore, it is wise to use the simple factory mode for some fixed and simple programs, and to use the simple factory mode for some complex programs that require frequent expansion. Programs use abstract factory pattern or factory method pattern.


For more articles on the singleton pattern and simple factory pattern in Java design pattern programming, please pay attention to the PHP Chinese website!

Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
2 weeks ago By 尊渡假赌尊渡假赌尊渡假赌
Repo: How To Revive Teammates
4 weeks ago By 尊渡假赌尊渡假赌尊渡假赌
Hello Kitty Island Adventure: How To Get Giant Seeds
4 weeks ago By 尊渡假赌尊渡假赌尊渡假赌

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

Top 4 JavaScript Frameworks in 2025: React, Angular, Vue, Svelte Top 4 JavaScript Frameworks in 2025: React, Angular, Vue, Svelte Mar 07, 2025 pm 06:09 PM

This article analyzes the top four JavaScript frameworks (React, Angular, Vue, Svelte) in 2025, comparing their performance, scalability, and future prospects. While all remain dominant due to strong communities and ecosystems, their relative popul

How do I implement multi-level caching in Java applications using libraries like Caffeine or Guava Cache? How do I implement multi-level caching in Java applications using libraries like Caffeine or Guava Cache? Mar 17, 2025 pm 05:44 PM

The article discusses implementing multi-level caching in Java using Caffeine and Guava Cache to enhance application performance. It covers setup, integration, and performance benefits, along with configuration and eviction policy management best pra

Node.js 20: Key Performance Boosts and New Features Node.js 20: Key Performance Boosts and New Features Mar 07, 2025 pm 06:12 PM

Node.js 20 significantly enhances performance via V8 engine improvements, notably faster garbage collection and I/O. New features include better WebAssembly support and refined debugging tools, boosting developer productivity and application speed.

How does Java's classloading mechanism work, including different classloaders and their delegation models? How does Java's classloading mechanism work, including different classloaders and their delegation models? Mar 17, 2025 pm 05:35 PM

Java's classloading involves loading, linking, and initializing classes using a hierarchical system with Bootstrap, Extension, and Application classloaders. The parent delegation model ensures core classes are loaded first, affecting custom class loa

Spring Boot SnakeYAML 2.0 CVE-2022-1471 Issue Fixed Spring Boot SnakeYAML 2.0 CVE-2022-1471 Issue Fixed Mar 07, 2025 pm 05:52 PM

This article addresses the CVE-2022-1471 vulnerability in SnakeYAML, a critical flaw allowing remote code execution. It details how upgrading Spring Boot applications to SnakeYAML 1.33 or later mitigates this risk, emphasizing that dependency updat

Iceberg: The Future of Data Lake Tables Iceberg: The Future of Data Lake Tables Mar 07, 2025 pm 06:31 PM

Iceberg, an open table format for large analytical datasets, improves data lake performance and scalability. It addresses limitations of Parquet/ORC through internal metadata management, enabling efficient schema evolution, time travel, concurrent w

How can I implement functional programming techniques in Java? How can I implement functional programming techniques in Java? Mar 11, 2025 pm 05:51 PM

This article explores integrating functional programming into Java using lambda expressions, Streams API, method references, and Optional. It highlights benefits like improved code readability and maintainability through conciseness and immutability

How to Share Data Between Steps in Cucumber How to Share Data Between Steps in Cucumber Mar 07, 2025 pm 05:55 PM

This article explores methods for sharing data between Cucumber steps, comparing scenario context, global variables, argument passing, and data structures. It emphasizes best practices for maintainability, including concise context use, descriptive

See all articles