Here is a good selection of four helpful sites for programmers.
This site is useful for implementing the online code without the need for an interpreter available for use in more than 75 programming languages and contains examples on the site.
An important website for the purpose of viewing and learning programming and designing websites and contains examples that can be applied online for the purpose of viewing or copying them.
I always use this website for founding the basic concept. I recommend you this site.
There is a site with the largest libraries that allow you to download a lot of ready-made codes that can be used in programming open-source Android applications.
This site includes many open source projects in many programming fields.