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

Based on @Staale's answer, and in an attempt not to rely on third party libraries, I would implement the File System approach by inspecting first package physical location with:

import java.io.File;
import java.io.FileFilter;
import java.util.ArrayList;
...
Class[] foundClasses = new Class[0];
final ArrayList> foundClassesDyn = new ArrayList>();

new java.io.File(
    klass.getResource(
        "/" + curPackage.replace( "." , "/")
    ).getFile()
).listFiles(
    new java.io.FileFilter() {
        public boolean accept(java.io.File file) {
            final String classExtension = ".class";

            if ( file.isFile()
                && file.getName().endsWith(classExtension)
                // avoid inner classes
                && ! file.getName().contains("$") )
            {
                try {
                    String className = file.getName();
                    className = className.substring(0, className.length() - classExtension.length());
                    foundClassesDyn.add( Class.forName( curPackage + "." + className ) );
                } catch (ClassNotFoundException e) {
                    e.printStackTrace(System.out);
                }
            }

            return false;
        }
    }
);

foundClasses = foundClassesDyn.toArray(foundClasses);