how to retrieve unique identifiers from android 11 r (API 30) device?

Question

I want to get unique identifiers like Android Device ID, IMEI, or MAC address from an Android phone with Android version 11 using Java.
Can someone help? I need just either one unique identifier.
This is the code that I use to get IMEI:

public String getIMEI() {
        Context context = null;
        TelephonyManager telephonyManager = (TelephonyManager) context.getSystemService(Context.TELEPHONY_SERVICE);
        Log.i("Testing: ", telephonyManager.getImei());
        return telephonyManager.getImei();
}

And this is the error message that I got:

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.String)' on a null object reference

Answer 1

As of the API 29, Google introduced new security policies to the TelephonyManager.getImei API. So it won't be available for 3rd party apps for security reasons.
Look at what is mentioned in the API's description:

Starting with API level 29, persistent device identifiers are guarded behind additional restrictions, and apps are recommended to use resettable identifiers (see Best practices for unique identifiers). This method can be invoked if one of the following requirements is met:

• If the calling app has been granted the READ_PRIVILEGED_PHONE_STATE permission; this is a privileged permission that can only be granted to apps preloaded on the device.
• If the calling app is the device owner of a fully-managed device, a profile owner of an organization-owned device, or their delegates (see DevicePolicyManager.getEnrollmentSpecificId()).
• If the calling app has carrier privileges (see hasCarrierPrivileges()) on any active subscription.
• If the calling app is the default SMS role holder (see RoleManager.isRoleHeld(java.lang.String)).
• If the calling app has been granted the Manifest.permission#USE_ICC_AUTH_WITH_DEVICE_IDENTIFIER permission.