为什么我得到“不能从静态上下文中引用的非静态变量"? [英] Why do I get "non-static variable this cannot be referenced from a static context"?

问题描述

我有一个非常简单的类，我想将其用作另一个类的子类.但是当我把它的代码放在父类中时，我得到:

I have a very simple class which I want to use as a subclass of another one. But when I put its code in the parent's class I get :

不能从静态上下文中引用的非静态变量

non-static variable this cannot be referenced from a static context

另一方面，当我将子类 GenTest 的类代码放在父类"类代码之外时 - JavaApp1 我没有收到此错误.

On the other hand when I put the sublass GenTest's class code outside the the "parent's" class code - JavaApp1 I do not get this error.

public class JavaApp1 {

    class GenTest {  
        @Deprecated
        void oldFunction() {
            System.out.println("don't use that");
        }
        void newFunction() {
            System.out.println("That's ok.");
        }
    }

    public static void main(String[] args) {
        GenTest x = new GenTest();
        x.oldFunction();
        x.newFunction();
    }
}

为什么会这样?

推荐答案

你的嵌套类(顺便说一下，它不是子类)没有被标记为静态的，因此它是一个inner 类，需要编码类 (JavaApp1) 的实例才能构造它.

Your nested class (which isn't a subclass, by the way) isn't marked as being static, therefore it's an inner class which requires an instance of the encoding class (JavaApp1) in order to construct it.

选项:

• 将嵌套类设为静态
• 使它不是内部类(即根本不在 JavaApp1 内)

• 创建一个 JavaApp1 的实例作为封闭实例":

• Make the nested class static
• Make it not an inner class (i.e. not within JavaApp1 at all)

• Create an instance of JavaApp1 as the "enclosing instance":

GenTest x = new JavaApp1().new GenTest();

我个人会采用第二种方法——Java 中的嵌套类有一些奇怪的地方，所以我会使用顶级类，除非你有充分的理由让它嵌套.(最后一个选项特别混乱，IMO.)

Personally I'd go with the second approach - nested classes in Java have a few oddities around them, so I'd use top-level classes unless you have a good reason to make it nested. (The final option is particularly messy, IMO.)

请参阅第 8.1 节.有关内部类的更多信息，请参阅 JLS 的 3.

这篇关于为什么我得到“不能从静态上下文中引用的非静态变量"?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！