what is activity https://www.runoob.com/android/android-acitivities.html

Chinese tutoral https://www.jianshu.com/p/a27f3ca027e3

https://www.youtube.com/watch?v=Fz_GT7VGGaQ

BluetoothDevice https://developer.android.com/reference/android/bluetooth/BluetoothDevice

scanResult https://developer.android.com/reference/android/bluetooth/le/ScanResult#getDevice()

example with video https://github.com/mitchtabian/Sending-and-Receiving-Data-with-Bluetooth/blob/master/Bluetooth-Communication/app/src/main/java/com/example/user/bluetooth_communication/BluetoothConnectionService.java

Bluetooth Chat example https://github.com/android/connectivity-samples/tree/master/BluetoothChat/#readme\

some odd examples https://github.com/search?q=Android-BLE-Connect-Example

https://github.com/joelwass/Android-BLE-Scan-Example

https://github.com/joelwass/Android-BLE-Connect-Example/blob/master/app/src/main/java/com/example/joelwasserman/androidbleconnectexample/MainActivity.java

https://github.com/adafruit/Bluefruit_LE_Connect_Android_v2

Beacon project https://stackoverflow.com/questions/37024547/can-android-device-run-bluetooth-le-in-peripheral-and-central-modes-at-the-same

example https://riptutorial.com/android/example/30768/using-a-gatt-server