是否可以通过类方法访问实例方法和变量 [英] is it possible to access instance methods and variable via class methods

问题描述

直到我在Oracle Doc上阅读了这本书(类方法无法直接访问实例变量或实例方法，它们必须使用对象引用)，这是我唯一了解的有关类无法访问实例方法和变量的信息(静态)方法.

Till I read this on Oracle Doc (Class methods cannot access instance variables or instance methods directly—they must use an object reference) the only thing I know, about instance methods and variables are not able to be accessed by the class(static) methods directly.

当说"....它们必须使用对象引用"时是什么意思?这是否意味着我们可以使用类方法间接访问实例变量和方法?

What does it mean when it says ....they must use an object reference? Does it mean we can access instance variables and methods indirectly using class methods?

先谢谢您.

推荐答案

这表示允许这样做:

public class Test {
    public int instanceVariable = 42;
    public void instanceMethod() {System.out.println("Hello!");}

    public static void staticMethod() {
        Test test = new Test();

        System.out.println(test.instanceVariable); // prints 42
        test.instanceMethod(); // prints Hello!
    }
}

这不是:

public class Test {
    public int instanceVariable = 42;
    public void instanceMethod() {System.out.println("Hello!");}

    public static void staticMethod() {
        System.out.println(instanceVariable); // compilation error
        instanceMethod(); // compilation error
    }
}

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