Get Bluetooth local mac address in Marshmallow

zmarties is right but you can still get the mac address via reflection or Settings.Secure:

  String macAddress = android.provider.Settings.Secure.getString(context.getContentResolver(), "bluetooth_address");

Access to the mac address has been deliberately removed:

To provide users with greater data protection, starting in this release, Android removes programmatic access to the device’s local hardware identifier for apps using the Wi-Fi and Bluetooth APIs.

(from Android 6.0 Changes)

You can access Mac address from the file "/sys/class/net/" + networkInterfaceName+ "/address" ,where networkInterfaceName can be wlan0 or eth1.But Its permission may be read-protected,so it may not work in some devices. I am also attaching the code part which i got from SO.

public static String getWifiMacAddress() {
        try {
            String interfaceName = "wlan0";
            List<NetworkInterface> interfaces = Collections
                    .list(NetworkInterface.getNetworkInterfaces());
            for (NetworkInterface intf : interfaces) {
                if (!intf.getName().equalsIgnoreCase(interfaceName)) {
                    continue;
                }

                byte[] mac = intf.getHardwareAddress();
                if (mac == null) {
                    return "";
                }

                StringBuilder buf = new StringBuilder();
                for (byte aMac : mac) {
                    buf.append(String.format("%02X:", aMac));
                }
                if (buf.length() > 0) {
                    buf.deleteCharAt(buf.length() - 1);
                }
                return buf.toString();
            }
        } catch (Exception exp) {

            exp.printStackTrace();
        } 
        return "";
    }

First the following permissions have to be added to Manifest;

<uses-permission android:name="android.permission.BLUETOOTH" />
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
<uses-permission android:name="android.permission.LOCAL_MAC_ADDRESS" />

Then,

public static final String SECURE_SETTINGS_BLUETOOTH_ADDRESS = "bluetooth_address";

String macAddress = Settings.Secure.getString(getContentResolver(), SECURE_SETTINGS_BLUETOOTH_ADDRESS);

After that the application has to be signed with OEM / System key. Tested and verified on Android 8.1.0.