Device id in android

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Java

Android

According to what i searched in google, android device ID is set once you boot the phone, and is reset when you reboot your phone or perform factory setting.

And it is what i think, you have a gmail account, you login that gmail account on your phone, visit google play store and download any app, then that gmail has a device id.

here is my question:

which one of the concept is right ?

Can i set it on my own by writing and android app .. or google doesn't allow me to do so ?


Thanks, any kind of help is appreciated...