类如何获取自身实例？Window.getWindow()实现疑问

Hey there! Let's unpack what's going on with that Window.getWindow() call and how a class can provide access to its own instance.

That line of code is almost certainly using the Singleton Pattern—a staple in game development (and software design in general) when you only want one instance of a class to exist. A game only needs one main window, right? So the Window class is designed to enforce that there's never more than one instance, and gives a global way to access it.

Here's what the missing Window class code probably looks like (this is the standard "eager initialization" singleton):

public class Window {
    // A static private instance that holds the single Window object
    private static Window instance = new Window();
    
    // Private constructor—this stops anyone outside the class from creating a new Window with `new Window()`
    private Window() {
        // This is where the window would be initialized: creating the OS window, setting resolution, etc.
    }
    
    // The public static method that lets other classes get the single instance
    public static Window getWindow() {
        return instance;
    }
    
    // Other window-related methods would go here, like `update()`, `render()`, or `getResolution()`
}

The key bits here are:

• The private constructor: No other class can instantiate Window directly.
• The static instance variable: It's created once when the Window class is loaded by the JVM.
• The static getWindow() method: It's the only way for other classes (like your ButtonEvent) to get access to that single Window instance.

Beyond the singleton pattern, there are a few common ways a class can provide access to its own instances:

• Lazy Initialization Singleton: If creating the Window is resource-heavy, you might wait to create it until it's first needed. This uses a synchronized method to avoid thread issues:

  public class Window {
      private static Window instance;
      
      private Window() {}
      
      public static synchronized Window getWindow() {
          if (instance == null) {
              instance = new Window();
          }
          return instance;
      }
  }
  

• Thread-Local Instances: For cases where each thread needs its own instance (unlikely for a game window, but useful in other scenarios), you can use ThreadLocal:

  public class SomeThreadSpecificClass {
      private static ThreadLocal<SomeThreadSpecificClass> instance = ThreadLocal.withInitial(SomeThreadSpecificClass::new);
      
      private SomeThreadSpecificClass() {}
      
      public static SomeThreadSpecificClass getInstance() {
          return instance.get();
      }
  }
  

• Static Factory Methods (Non-Singleton): If you want to control instance creation but allow multiple instances, a static factory method can handle that (e.g., returning new instances or reusing a pool):

  public class GameObject {
      private GameObject() {}
      
      public static GameObject createNew() {
          return new GameObject();
      }
  }
  

In your game engine tutorial, the Window class is almost definitely using the singleton pattern. The blogger might have skipped showing it because they assumed familiarity with the pattern, or maybe covered it in an earlier video you missed.

内容的提问来源于stack exchange，提问作者Kenneth