The negative pattern is simply a different way to print out negative numbers. You may want a wide variety of choices:
1,234 1,234 1,234 1,234 CR
-1,234 1,234- (1,234) 1,234 DR
and so on. Each of these is useful in their different domains. The (1,234)
variant is actually quite useful if you don't have a colour printer since it stands out a lot more than just a leading negative and it's used quite a bit in bookkeeping and accounting areas.
My own favorite (in a non-Java setting, Libre Office) is:
"#,##9.99 ;[RED](#,##9.99-)"
which outputs the negative numbers in red with a trailing -
sign and surrounded by parentheses, so there's no doubt it's a negative value: