what does example.split mean in java

Example 1: split on . in java

String textfile = "ReadMe.txt";
String filename = textfile.split(".")[0];
String extension = textfile.split(".")[1];

Example 2: split on . in java

String textfile = "ReadMe.txt";
String filename = textfile.split("\\.")[0];
String extension = textfile.split("\\.")[1];