Can you find all classes in a package using reflection?

Question

Is it possible to find all classes or interfaces in a given package? (Quickly looking at e.g. Package, it would seem like no.)

Answer 1

It is very possible, but without additional libraries like Reflections it is hard...
It is hard because you haven't full instrument for get class name.
And, I take the code of my ClassFinder class:

package play.util;

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.List;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;

/**
 * Created by LINKOR on 26.05.2017 in 15:12.
 * Date: 2017.05.26
 */
public class FileClassFinder {
private JarFile file;
private boolean trouble;
public FileClassFinder(String filePath) {
    try {
        file = new JarFile(filePath);
    } catch (IOException e) {
        trouble = true;
    }
}

public List findClasses(String pkg) {
    ArrayList classes = new ArrayList<>();
    Enumeration entries = file.entries();
    while (entries.hasMoreElements()) {
        JarEntry cls = entries.nextElement();
        if (!cls.isDirectory()) {
            String fileName = cls.getName();
            String className = fileName.replaceAll("/",         ".").replaceAll(File.pathSeparator, ".").substring(0, fileName.lastIndexOf('.'));
            if (className.startsWith(pkg)) classes.add(className.substring(pkg.length() + 1));
        }
    }
    return classes;
}
}