如何重写抽象内部类的方法？
我的代码是：
core/Base.java
package core;
public class Base {
public abstract class AbstractInner {
abstract void run();
}
}
Test.java
class Test extends core.Base {
class Inner extends AbstractInner {
void run() {}
}
}
javac 抱怨如下；
shell> javac -cp . Test.java
Test.java:2: Test.Inner is not abstract and does not override abstract method run() in core.Base.AbstractInner
class Inner extends AbstractInner {
^
我的错误是什么？
如果Base和Test在同一个包中，则编译成功。我不知道为什么。
My codes are:
core/Base.java
package core;
public class Base {
public abstract class AbstractInner {
abstract void run();
}
}
Test.java
class Test extends core.Base {
class Inner extends AbstractInner {
void run() {}
}
}
javac complains like the following;
shell> javac -cp . Test.java
Test.java:2: Test.Inner is not abstract and does not override abstract method run() in core.Base.AbstractInner
class Inner extends AbstractInner {
^
What is my mistake?
If Base is in the same package as Test, compile is successful. I don't know why.
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评论（1）
有一些非直观的规则来管理包私有成员的重写。本质上，如果重写的类位于同一个包中，则可以重写包私有方法。如果不是，则它无法看到
AbstractInner的run()声明，因此无法覆盖它。相反，您正在声明一个具有相同签名的新方法。如果您在
AbstractInner中将run()设为受保护（或公共）（因此也在Inner中），而不是使用默认可见性，则它将按预期工作。回想一下，只有在接口中才隐式声明方法
public。在抽象类中，它们隐式是包私有的。There are some non-intuitive rules governing overridibility of package-private members. Essentially, you can override a package-private method if the overriding class is in the same package. If it's not, it does not have visibility to see
AbstractInner's declaration ofrun()and so can't override it. Instead you are declaring a new method with the same signature.If you make
run()protected (or public) inAbstractInner(and thus inInneras well) instead of using the default visibility, it will work as intended.Recall that only in interfaces are declared methods implicitly
public. In abstract classes, they are implicitly package-private.