为什么我得到“非静态变量这不能从静态上下文引用”？ [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，我想使用作为另一个的子类。但是当我把它的代码放在父类的类中我得到：

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 :

非静态变量这不能从静态上下文引用

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

另一方面，当我把子类 GenTest parent's类代码 - 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();
    }
}

为什么会发生这种情况？

Why is this happening ?

推荐答案

您的嵌套类（不是一个子类）标记为静态，因此它是一个内类，它需要一个编码类（JavaApp1）的实例来构建它。

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.

：

• 设置嵌套类static


• 使其不是内部类code> JavaApp1 ）



• 创建 JavaApp1 的实例封装实例：

• 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();

- Java中的嵌套类在它们周围有一些奇怪的东西，所以我会使用顶级类，除非你有一个很好的理由让它嵌套。 （最后一个选项特别凌乱，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.)

查看 JLS的第8.1.3节有关内部类的更多信息。

See section 8.1.3 of the JLS for more information about inner classes.

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