列出从另一个类继承的类的类型

Question

So, this is probably a simple question because I'm only missing a command here. How can I list all the types of those classes that inherit from a specific class. Or formulated another way: How can I list the type of all child-classes from a class?

public class person {

    person()   
    {     
        listChilds(this);   
    } 
}

listChilds in this case would produce a list that would probably contain classes like teacher , footballPlayer , student , plumber , etc. The getClass() command of all the subclasses basically.

Is there actually a way to do this?

Answer 1

It is impossible because a class does not know who inherits it. See oracle docs , here you can see the basic concept behind what you are trying to do.

Answer 2

While you cannot on-demand know of the classes that extend it, you can be slightly sneaky and cache anything that utilizes its constructor:

public class Inheritance {

    public Inheritance() {
        System.out.println(this.getClass().getName());
    }

    public static void main(String[] args) {
        Testing test = new Testing();
    }

}

class Testing extends Inheritance {

    public Testing() {
        super();
    }

}

Would print "Testing", using the this.getClass() in the super constructor will return a Class<?> instance of the class that is extending it.

Answer 3

It's rather easy with http://code.google.com/p/reflections/ . This snippet lists all subclasses of JPanel , for example:

import java.util.Set;

import javax.swing.JPanel;

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

public class SubtypesReflectionsTest
{
    public static void main(String[] args)
    {
        Class<?> c = JPanel.class;
        Reflections reflections = new Reflections(
            "", ClasspathHelper.forClass(c),
            new SubTypesScanner(false));
        Set<?> subTypes = reflections.getSubTypesOf(c);
        for (Object element : subTypes)
        {
            System.out.println("Class "+element);
        }
    }
}

But I agree with the comments: You should really think about what you are doing there, and if there is no more appropriate way to achieve your goal.