FULL PRODUCT VERSION:

java -version
java version "1.8.0_361"
Java(TM) SE Runtime Environment (build 1.8.0_361-b09)
Java HotSpot(TM) 64-Bit Server VM (build 25.361-b09, mixed mode)

OS VERSION:

sw_vers
ProductName: macOS
ProductVersion: 13.3.1
ProductVersionExtra: (a)
BuildVersion: 22E772610a


A DESCRIPTION OF THE PROBLEM :
getCanonicalHostName returns ip address in macOS instead of fully qualified domain name.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :

Followed these documents to check the macOS machine host name
https://support.apple.com/en-in/guide/mac-help/mchlp2322/mac
https://support.apple.com/en-in/guide/mac-help/mh27452/13.0/mac/13.0

If we verify the macOS machine name it with scutil command we can see the host name.

 scutil --get HostName
bishnaya-mac
 scutil --get LocalHostName
bishnaya-mac
 scutil --get ComputerName
bishnaya-mac

If we run the below code it returns ip address
============code==================
import java.net.InetAddress;
import java.net.UnknownHostException;

public class MachineName {

    public static void main(String arg[]) throws UnknownHostException {

        String canHostName = InetAddress.getLocalHost().getCanonicalHostName();
        System.out.println("Canonical Host Name : "+canHostName);

    }
}

===========================================

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED - Canonical Host Name : bishnaya-mac
ACTUAL - Canonical Host Name : ip_address_of_machine