java 从另一个类访问在主类中创建的对象方法

Access an object method created in main class from another class

提问by Rias

Is it possible to access an object created in main class? or there is a way of get the owner/reference class?

是否可以访问在主类中创建的对象？或者有没有办法获得所有者/引用类？

For example, in the code below, how can I call the method setMenu, that is on the myMainClass, from one of the Menuclass objects (firstMenu, secondMenu)

例如，在下面的代码中，如何从Menu类对象之一（firstMenu、secondMenu）调用myMainClass上的setMenu方法

I can make the Menu objects static but doesn't seems like the right approach...

我可以将 Menu 对象设为静态，但似乎不是正确的方法...

Main Class

主班

public class myMainClass extends JFrame {

    JPanel container;
    Menu firstMenu;
    Menu secondMenu;

    myMainClass() {

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(400, 400);

        firstMenu = new Menu();
        secondMenu = new Menu();

        container = new JPanel(new CardLayout());
        container.add(firstMenu, "firstMenu");
        container.add(secondMenu, "secondMenu");

        add(container);
    }

    public void setMenu(String s) {
        CardLayout cl = (CardLayout) (container.getLayout());
        cl.show(container, s);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                myMainClass myMainClassObject = new myMainClass();
                myMainClassObject.setVisible(true);
            }
        });
    }
}

Menu Class

菜单类

public class Menu extends JFrame {

    Menu() {
        //How can I call myMainClass setMenu method from here?
        //myMainClass.setMenu("secondMenu");
        //myMainClassObject.setMenu("secondMenu");
    }
}

Thanks

谢谢

采纳答案by adarshr

You've answered your own question. Make the setMenumethod static.

你已经回答了你自己的问题。使setMenu方法静态。

public void setMenu(String s) {
        CardLayout cl = (CardLayout) (container.getLayout());
        cl.show(container, s);
    }

And invoke it using the class name MyMainClass.setMenuin the Menuclass.

并使用类MyMainClass.setMenu中的Menu类名调用它。

Otherwise, you'll have to pass the instance of MyMainClassto the Menuclass by overloading its constructor.

否则，您必须通过重载其构造函数将 的实例传递MyMainClass给Menu类。

firstMenu = new Menu(this);
secondMenu = new Menu(this);

And in the other class,

而在另一个班级，

public class Menu extends JFrame {

    Menu() {
        //How can I call myMainClass setMenu method from here?
        //myMainClass.setMenu("secondMenu");
        //myMainClassObject.setMenu("secondMenu");
    }

    Menu(MyMainClass main) {
        main.setMenu("secondMenu");
    }
}

回答by Maricel

setMenu() is an instance method if you want to call it you would need to instantiate myMainClass, which btw should be called MyMainClass, so you need to do:

setMenu() 是一个实例方法，如果你想调用它，你需要实例化 myMainClass，顺便说一下，它应该被称为 MyMainClass，所以你需要这样做：

MyMainClass mainClass = new MyMainClass();
mainClass.setMenu("secondMenu");

If you want the method to be accessed via the class then you would need to create the method static, so it is a class method and not an instance method, so you can call it like:

如果您希望通过类访问该方法，则需要创建静态方法，因此它是类方法而不是实例方法，因此您可以像这样调用它：

MyMainClass.setMenu("secondMenu");