可以在Java中更改内部类的外部类实例吗？ [英] Possible to change the outer class instance of an inner class in Java?

问题描述

在Java中，每当创建内部类实例时，它都与外部类的实例相关联。出于好奇，是否可以将内部类与外部类的另一个实例相关联？

In Java, whenever an inner class instance is created, it is associated with an instance of an outer class. Out of curiosity, is it possible to associate the inner class with another instance of an outer class instead?

推荐答案

是的，这是可能，虽然这对我来说听起来真的很糟糕。我的想法是使用反射设置否则 final 指向外部实例的指针（不能保证成功）。

Yes, this is possible, although it sounds like a really bad idea to me. The idea is to set the otherwise final pointer to the outer instance using reflection (which is not guaranteed to succeed).

import java.lang.reflect.*;

public class Me {
    final String name;

    Me(String name) {
        this.name = name;
    }

    class InnerMe {     
        String whoAreYou() {
            return name;
        }
    }   

    InnerMe innerSelf() {
        return new InnerMe();
    }

    public static void main(String args[]) throws Exception {
        final Me me = new Me("Just the old me!");
        final InnerMe innerMe = me.innerSelf();
        System.out.println(innerMe.whoAreYou()); // "Just the old me!"
        Field outerThis = innerMe.getClass().getDeclaredFields()[0];
        outerThis.setAccessible(true);
        outerThis.set(innerMe, new Me("New and improved me!"));
        System.out.println(innerMe.whoAreYou()); // "New and improved me!"
    }

}

这里的关键部分是 outerThis.setAccessible（true）; - a SecurityManager 可以强制执行禁止此功能成功的策略。

The crucial part here is outerThis.setAccessible(true); -- a SecurityManager could enforce a policy that prohibits this from succeeding.

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