还要注意的是，这当然只能找到当前类路径中存在的所有子类。想必这对于你目前所看到的是可以的，而且你也有可能考虑过这一点，但如果你在任何时候发布了一个非最终类(对于不同程度的“狂野”)，那么其他人已经编写了他们自己的子类，而你不知道这是完全可行的。

Thus if you happened to be wanting to see all subclasses because you want to make a change and are going to see how it affects subclasses' behaviour - then bear in mind the subclasses that you can't see. Ideally all of your non-private methods, and the class itself should be well-documented; make changes according to this documentation without changing the semantics of methods/non-private fields and your changes should be backwards-compatible, for any subclass that followed your definition of the superclass at least.

如果你想加载给定类在同一个包中的所有子类，你可以这样做:

public static List<Class> loadAllSubClasses(Class pClazz) throws IOException, ClassNotFoundException {
    ClassLoader classLoader = pClazz.getClassLoader();
    assert classLoader != null;
    String packageName = pClazz.getPackage().getName();
    String dirPath = packageName.replace(".", "/");
    Enumeration<URL> srcList = classLoader.getResources(dirPath);

    List<Class> subClassList = new ArrayList<>();
    while (srcList.hasMoreElements()) {
        File dirFile = new File(srcList.nextElement().getFile());
        File[] files = dirFile.listFiles();
        if (files != null) {
            for (File file : files) {
                String subClassName = packageName + '.' + file.getName().substring(0, file.getName().length() - 6);
                if (! subClassName.equals(pClazz.getName())) {
                    subClassList.add(Class.forName(subClassName));
                }
            }
        }
    }

    return subClassList;
}

除了你所描述的，没有别的办法了。想想看——如果不扫描类路径上的每个类，如何知道哪些类扩展了ClassX ?

Eclipse只能在看起来“有效”的时间内告诉您关于父类和子类的信息，因为在您按下“显示在类型层次结构中”按钮时，它已经加载了所有类型数据(因为它一直在编译您的类，知道类路径上的所有内容，等等)。

我需要将此作为一个测试用例，以查看是否向代码中添加了新的类。这就是我所做的

final static File rootFolder = new File(SuperClass.class.getProtectionDomain().getCodeSource().getLocation().getPath());
private static ArrayList<String> files = new ArrayList<String>();
listFilesForFolder(rootFolder); 

@Test(timeout = 1000)
public void testNumberOfSubclasses(){
    ArrayList<String> listSubclasses = new ArrayList<>(files);
    listSubclasses.removeIf(s -> !s.contains("Superclass.class"));
    for(String subclass : listSubclasses){
        System.out.println(subclass);
    }
    assertTrue("You did not create a new subclass!", listSubclasses.size() >1);     
}

public static void listFilesForFolder(final File folder) {
    for (final File fileEntry : folder.listFiles()) {
        if (fileEntry.isDirectory()) {
            listFilesForFolder(fileEntry);
        } else {
            files.add(fileEntry.getName().toString());
        }
    }
}

不要忘记，为类生成的Javadoc将包括一个已知子类列表(对于接口，包括已知实现类)。

还要注意的是，这当然只能找到当前类路径中存在的所有子类。想必这对于你目前所看到的是可以的，而且你也有可能考虑过这一点，但如果你在任何时候发布了一个非最终类(对于不同程度的“狂野”)，那么其他人已经编写了他们自己的子类，而你不知道这是完全可行的。

Thus if you happened to be wanting to see all subclasses because you want to make a change and are going to see how it affects subclasses' behaviour - then bear in mind the subclasses that you can't see. Ideally all of your non-private methods, and the class itself should be well-documented; make changes according to this documentation without changing the semantics of methods/non-private fields and your changes should be backwards-compatible, for any subclass that followed your definition of the superclass at least.