How does split work in java code example

Example 1: java split string

String yourString = "Hello/Test/World";
String[] strings = yourString.split("/" /*<- Regex */); 

Output:
strings = [Hello, Test, World]

Example 2: split on . in java

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