New to Java

Hi all
I have two similar code below:

public class Test {

    public static void main(String[] args) {
        String ip  = "192,168,30,153";//comma
        
        String[] ss = ip.split(",");   //it's comma
        for(String s:ss){
        	System.out.println(s);
        }
     }
}

the result is :
192
168
30
153

but when it changs to period nothing printed.

public class Test {

    public static void main(String[] args) {
        String ip  = "192.168.30.153";//period
        
        String[] ss = ip.split(".");   //it's period
        for(String s:ss){
        	System.out.println(s);
        }
     }
}

thanks