Refactoring by passing generic method

I have simplified my code to this:

static private String waitForString(String expected, int attempts) {
  String actual = null;
   for (int i = 0; i < attempts; i++){
      actual = getString();
      if (validateString(actual, expected)) {
         return actual;
      }
   }
   return null;
}

static private int waitForInt(int expected, int attempts) {
   int actual = 0;
   for (int i = 0; i < attempts; i++){
      actual = getInt();
      if (validateInt(actual, expected)) {
         return actual;
      }
   }
   return 0;
}

Since I'm using the same loop (and since I have more than one class with more than one corresponding "getter" method and validation method) I would like to refactor it. I tried this:

static <T> T helperMethod(Method getMethod, Method validator,T expected, int attempts) {
   T actual = null;
   for (int i = 0; i < attempts; i++){
      actual = method.invoke(null);
      if (validator.invoke(null, actual, expected)) {
         return actual;
      }
   }
   return null;
}

However I'm getting following errors:

actual = method.invoke(null);
error: incompatible types: Object cannot be converted to T 

validator.invoke(null, actual, expected)
error: incompatible types: Object cannot be converted to boolean 

Can I specify in the function declaration only to accept methods with the correct return type? If so, how? Ideas for other ways to refactor will be appreciated.