Write a program in Dart to check if a given string is a valid URL

Here's an example program in Dart to check if a given string is a valid URL using regular expressions: ``` void main() { String url = 'https://www.example.com'; bool isValid = Uri.parse(url).isAbsolute; if (isValid) { print('$url is a valid URL'); } else { print('$url is not a valid URL'); } } ``` This program checks if the string `url` is a valid URL by parsing it with the `Uri` class and checking whether it is an absolute URI using the `isAbsolute` property. If `isAbsolute` returns `true`, then the URL is considered valid.