为什么reflections.getSubTypesOf（Object.class）找不到枚举？

问题描述

如果我有

Reflections reflections = new Reflections("my.package", classLoader, new SubTypesScanner(false));

然后找到我的枚举类

Set<Class<? extends Enum>> enums = reflections.getSubTypesOf(Enum.class);

但这不是

Set<Class<?>> classes = reflections.getSubTypesOf(Object.class);

这是否有原因？

可重现的示例：

package cupawntae;

import org.reflections.Reflections;
import org.reflections.scanners.SubTypesScanner;

public class Reflector {
    public static void main(String[] args) {
        Reflections reflections = new Reflections("cupawntae", Reflector.class.getClassLoader(), new SubTypesScanner(false));
        System.out.println("Objects: " + reflections.getSubTypesOf(Object.class));
        System.out.println("Enums: " + reflections.getSubTypesOf(Enum.class));
        System.out.println("Enum's superclass: " + Enum.class.getSuperclass());
    }
}

枚举类别：

package cupawntae;

public enum MyEnum {
}

输出：

Objects: [class cupawntae.Reflector]
Enums: [class cupawntae.MyEnum]
Enum's superclass: class java.lang.Object

推荐答案

这实际上是，尽管可以说不是特别清楚或直观：

This is actually documented behaviour, although it's arguably not particularly clear or intuitive:

edit：：

在这种情况下， java.lang.Enum 被视为传递类（例如 other.package.OtherClass ），因此不包括在扫描中，这意味着<$ c $的子类c>枚举不包括在内。

In this case java.lang.Enum counts as a transitive class (like other.package.OtherClass), and is therefore not included in the scan, meaning subclasses of Enum are not included.

类似地，如果我们在 Reflections 中进行问题的示例在目标包之外扩展了某些内容，例如

Similarly, if we make Reflections in the question's example extend something outside the target package, e.g.

public class Reflector extends Exception {

然后在扫描中不再找到该类

then the class is no longer found in the scan

Objects: []
Enums: [class cupawntae.MyEnum]
Enum's superclass: class java.lang.Object

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