java - 相同(？)对象的不同对象引用

Question

我最近问过关于从另一个类获取类的唯一实例的问题。

( How to get specific instance of class from another class in Java? )

所以，我正在努力让它发挥作用:

我的申请:

public class Application
{

    // I will always have only one instance of Application

    private static Application _application;

    // Every instance of Application (one in my case) should have its own View

    private View view;

    // Constructor for new instance of Application

    private Application()
    {
        view = new View();
    }

    // Getter for my unique instance of Application

    public static Application getSharedApplication()
    {
        if (_application == null)
            _application = new Application();
        return _application;
    }

    // Main class

    public static void main(String[] args)
    {
        // So I'm accessing my instance of Application
        Application application1 = getSharedApplication();

        // Here is object reference
        System.out.println(application1);

        // And now I'm accessing the same instance of Application through instance of View
        Application application2 = application1.view.getApplication();

        // Here is object reference
        System.out.println(application2);
    }

}

我的 View :

public class View
{

    // I'm accessing my instance of Application again

    public static Application application = Application.getSharedApplication();

    // This method should return my unique instance of Application

    public Application getApplication()
    {
        return application;
    }

}

问题是 main 方法返回不同的对象引用。

Application@1430b5c
Application@c2a132

我的代码有什么问题？

Answer 1

这是发生了什么:

• 程序首先调用Application application1 = getSharedApplication();
• 然后调用调用 new Application() 的静态方法 - 该调用需要加载 View 类，它是 Application 的成员。
• View 类已加载，其静态成员已初始化并运行 getSharedApplication();(请注意，在此阶段，_application 仍为 null)。这也创建了一个 new Application()

您现在有 2 个应用程序实例。

请注意，如果您将 View v = new View(); 添加为 main 的第一行，您只有一个 Application 实例(从 View 的静态变量加载一次) .当您认真思考但不是很直观时，这是有道理的...