boolean[] board = new boolean[10_00_001]; (Souce editorial)
why used underscore here
and why error is not occuring
Boolean array init
A new feature was introduced by JDK 7 which allows to write numeric literals using the underscore character. Numeric literals are broken to enhance the readability.
This feature enables us to separate groups of digits in numeric literals, which improves readability of code. For instance, if our code contains numbers with many digits, we can use an underscore character to separate digits in groups of three, similar to how we would use a punctuation mark like a comma, or a space, as a separator.