code: public void instrumentClassFile(File classfile) throws IOException {
          FileInputStream fis = new FileInputStream(classfile);
          byte[] bytes = transform(fis);
          fis.close();
          fis = null;
  
          // If the class was successfully transformed, rewrite it
          if (bytes != null) {
              FileOutputStream fos = new FileOutputStream(classfile);
              fos.write(bytes);
              fos.close();
          }
      }
docs: Instrument the specified class file.