I'm studying a Java code that uses the regular expression "( *|)". What does the pipe do in this expression?
So far I understood it works the same way as the expression for a group of optional spaces, i.e. "( *).
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Jindřich Mynarz
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zero or more spaces OR nothing = zero or more spaces – Avinash Raj Jan 12 '18 at 10:49
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If you paste that in https://regex101.com/ you get a description of what each bit does on the right – apokryfos Jan 12 '18 at 10:49
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Well I think the RHS of that alternation is empty, i.e. we could just use `\s*` and have the same effect. – Tim Biegeleisen Jan 12 '18 at 10:50
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2@TimBiegeleisen ` *` and `\s*` is not the "same effect". – laune Jan 12 '18 at 10:51
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@laune Yes I know, but the only way to write zero or more _spaces_ would be `[ ]*` and it still be readable, and I didn't want to throw off the OP. – Tim Biegeleisen Jan 12 '18 at 10:53
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Why do you need the brackets for space, a single character? No functional purpose, only for readability? – Jindřich Mynarz Jan 12 '18 at 11:04
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Pipe ('|') simply means 'or'. At the one side we have regex for zero or more spaces, on the other side we have nothing - so it will match zero or more spaces or an empty string.
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1That confirms my assumption that the pipe is useless in this regular expression, right? – Jindřich Mynarz Jan 12 '18 at 11:02
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