如何从Java中的另一个类获取类的特定实例？ [英] How to get specific instance of class from another class in Java?

问题描述

我使用 main 方法创建了下面的类，它创建了 Application 的新实例， ApplicationModel ， ApplicationView 和 ApplicationController $ c> Application 。

  public class Application 
 {
 
 //变量
 
 private ApplicationSettings设置; 
 private ApplicationModel model; 
 private ApplicationView视图; 
 private ApplicationController controller; 
 
 //构造函数
 
 public Application（）
 {
 settings = new ApplicationSettings（）; 
 model = new ApplicationModel（）; 
 view = new ApplicationView（model）; 
 controller = new ApplicationController（）; 
} 
 
 //主方法
 
 public static void main（String [] args）
 {
应用程序应用程序）; 
} 
 
 //应用程序的设置，模型，视图，控制器的获取器
 
} 
  pre> 
 
 
我知道， Application 只会有一个唯一的实例。
 
 
 
而我想在我的 ApplicationModel ， ApplicationView  code> ApplicationController 类。
 
 
 
如何实现？
解决方案
我将在Application类上使用单例。
 
 
 
放置一个 public static 方法返回您的唯一应用程序实例。
  public class Application 
 {
 private Application ）{} //使你的构造函数私有，所以只有war 
 //访问应用程序是通过单例模式
 
 private static Application _app; 
 
 public static Application getSharedApplication（）
 {
 if（_app == null）
 _app = new Application（）; 
 return _app; 
} 
} 
  
您可以阅读更多关于 singleton设计模式 此处。 
 
 
 
每当您需要一个且只有 Application 实例时，您可以执行：
 应用程式app = Application.getSharedApplication（）; 
  
 
I've created the following class with the main method, which creates new instance of Application and instances of ApplicationModel, ApplicationView and ApplicationController for this particular Application.
public class Application
{

    // Variables

    private ApplicationSettings         settings;
    private ApplicationModel            model;
    private ApplicationView             view;
    private ApplicationController       controller;

    // Constructor

    public Application()
    {
        settings        = new ApplicationSettings();
        model           = new ApplicationModel();
        view            = new ApplicationView(model);
        controller      = new ApplicationController();
    }

    // Main method

    public static void main(String[] args)
    {
        Application application = new Application();
    }

    // Getters for settings, model, view, controller for instance of Application

}
I know, that there will always be only one unique instance of Application.

And I want to get this particular instance in my ApplicationModel, ApplicationView and ApplicationController classes.

How is it possible?
解决方案
I would use a singleton on Application class.

Put a public static method to return your one and only application instance.
public class Application
{
    private Application() { } // make your constructor private, so the only war
                              // to access "application" is through singleton pattern

    private static Application _app;

    public static Application getSharedApplication() 
    {
        if (_app == null)
            _app = new Application();
        return _app;
    }
}
You can read more about singleton design pattern here. 

Every time you need the one and only Application instance, you do:
Application app = Application.getSharedApplication();


                        
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