Dart is quite similar to Java. If you are already familiar with Java I believe it will take you very little time to get started with Dart.

FWIW, I was able to write two small but useful program in Dart in one day, without any experience with the language at all:

- A script to convert CSV file to SELECT ... UNION ALL SELECT ... statements

- A script to parse my timesheet (in Emacs' org-mode) & insert it into my client's timesheet database

I just used these 3 resources:

[1] Dart language tour https://www.dartlang.org/guides/language

[2] Standard library introduction https://www.dartlang.org/guides/libraries

[3] Standard library reference (like JavaDocs) https://api.dartlang.org/stable/1.24.2/index.html

[4] And the pub package manager https://www.dartlang.org/tools/pub