One of the greatest way to learn code, is to learn from masters, from people who are actively engaged in development and coding.
Here I am listing the repositories which an AEM developer can look into to refer code and to learn new coding patterns and enhancements in coding languages :
In no way this list is complete. I will try to add more repos. as I come across and remember.
To watch any changes in above repos. create an account in github and use “Watching” option.
If you know any repo. which will be helpful for an AEM developer, it will be great if you can leave a comment of same.