java – 相同(？)对象的不同对象引用

我最近问过从另一个班级获取类的唯一实例.

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

所以,我试图让它工作：

我的应用程序：

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);
    }

}

我的看法：

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

我的代码出了什么问题？

最佳答案

这是发生的事情：

>程序首先调用Application application1 = getSharedApplication();
>它反过来调用调用new Application()的静态方法 – 该调用需要加载View类,它是Application的成员.
>加载View类并初始化其静态成员并运行getSharedApplication(); (请注意,在此阶段,_application仍为null).这也创建了一个新的Application()

您现在有2个应用程序实例.

请注意,如果添加View v = new View();作为main的第一行,您只有一个Application实例(从View的静态变量中加载一次).当你仔细思考但不是很直观时,这是有道理的…