Class Loader Example: Load Class "By Hand" to "Unrotate" Bytes

// Apply (for example) as follows:
//    java ReflectionTest Hello 1
import java.io.*;
import java.lang.reflect.*;

class CryptClassLoader extends ClassLoader {
   Class cls;
   
   public Class returnClass () {
      return cls;
   }

   public CryptClassLoader (String classname, int key) {
      try {
         FileInputStream in = new FileInputStream (classname+".class");
         ByteArrayOutputStream buffer = new ByteArrayOutputStream();
         int ch;
         while ((ch = in.read()) != -1) {
            buffer.write((ch + (256 - key)) % 256);
         }
         byte [] rec = buffer.toByteArray();
         cls = defineClass (classname, rec, 0, rec.length);
      }
      catch (Exception e) {
         System.out.println("File not found "+e);
      }
   }
}

public class ReflectionTest {
   public static void main (String a[]) {
      try {
         int key = Integer.parseInt(a[1]);
         String classname = a[0];
         
         // ----------------------------------
         //   Class cl = Class.forName(classname);  // Can't use this - must use next two lines
         // ----------------------------------

         CryptClassLoader loader = new CryptClassLoader(classname, key);
         Class cl = loader.returnClass();
         
         //-----------------------------------------------------------------------------------------
         // Next two lines could be used here instead of following four
         // ----------------------------------------------------------
         // Method m = cl.getMethod("sayHello", null);  // Class[] { } not needed
         // m.invoke(null, null);  // Hello obj, Object[] { } not needed (static method and no args)
         //-----------------------------------------------------------------------------------------

         Constructor ct = cl.getConstructor ( null );
         Object obj = ct.newInstance ( null );
         Method m = cl.getMethod("sayHello", null);  // Class[] { } not needed
         m.invoke(obj, null);  // Object[] { } not needed (no args to method)
      }
      catch (Exception e) {
         System.out.println(e); 
      }
   }
}