Why I avoid android.util.Patterns

I wanted to leave a quick note about android.util.Patterns: I think it's a dangerously misleading class.

It's so tempting - who wouldn't want ready-made, AOSP-approved regexes? But there's some serious problems with Patterns:

1. Regarding Patterns.EMAIL_ADDRESS: I'm against using complex regexes to validate emails. It's a surprisingly difficult problem and chances are you will get it wrong.

2. Patterns.IP_ADDRESS only applies to IPv4, so it's misleading.

3. Patterns.TOP_LEVEL_DOMAIN will grow increasingly irrelevant in a world where you can register your own TLDs.

4. Both Patterns.WEB_URL and Patterns.DOMAIN_NAME
   depend on Patterns.TOP_LEVEL_DOMAIN. Ouch!

5. The docs admit that Patterns.PHONE is just a heuristic and will miss legitimate phone numbers, so it can't be used for validation.

There are so many caveats to be had with Patterns that you're better off specifying your own regexes for your use case.