Use Android MAC address as unique identifier

I've been reading some posts on stack overflow where Android doesn't have a unique identifier. But can't I use the MAC address of the device as the unique ID? If not, why not? If so, does anyone know how to get it programmatically (i.e. a piece of code [please])?

For reference:

My application needs a network, so devices without a network will not be able to install it

resolvent:

Not 100% reliable

Here is what Google has to say on the subject：

In addition, you assume that all devices will accurately report the MAC address in some way. I think a custom ROM, perhaps a root device, may cheat the MAC address. This may or may not be your concern - I just point out

At best, it may need WiFi. It cannot ask to turn on WiFi

See this answer