Digit grouping for very long numbers in Java

When we need to write a Billion on a sheet of paper we don't just write 1000000000, because it is hard to see if it is exactly a billion or  hundred million in the very first glance without counting the digits. Instead, grouping the digits is common practice so it can be written as 1,000,000,000. It is evident that grouping the digits improves the readability of numbers.

    However, all these days I never saw anywhere grouping the numeric literals in the software code.  Recently I was surprised to see that Java language supports digit groups by using the underscore ('_') characters as group separators. For example, the following is a perfectly valid way to store a decimal Billion in java.

int n = 1_000_000_000;