Code name   Version     API level
Oreo        8.0         API level 26
Nougat      7.1         API level 25
Nougat      7.0         API level 24

You should check Build.VERSION.SDK_INT >25

The “O” version is a provisional API level that is usable only for development and testing during the Android O Developer Preview.

Code name   Version     API level
Oreo        8.0         API level 26
Nougat      7.1         API level 25
Nougat      7.0         API level 24

You should check Build.VERSION.SDK_INT >= Build.VERSION_CODES.N

The “O” version is a provisional API level that is usable only for development and testing during the Android O Developer Preview.

Code name   Version     API level
Nougat      7.1         API level 25
Nougat      7.0         API level 24

You should check Build.VERSION.SDK_INT >= 24

Code name   Version     API level
Oreo        8.0         API level 26
Nougat      7.1         API level 25
Nougat      7.0         API level 24

You should check Build.VERSION.SDK_INT >25

The “O” version is a provisional API level that is usable only for development and testing during the Android O Developer Preview.