code: private Method findCallbackMethod(final Class<?> klass, final String signature) {
          for (Method method : klass.getMethods()) {
  
              if (method.toString().equals(signature)) {
                  // found!
                  return method;
              }
          }
  
          throw new JsiiException("Unable to find callback method with signature: " + signature);
      }
docs: Finds the Java method that implements a callback.
  @param klass The java class.
  @param signature Method signature
  @return a {@link Method}.