java - regex for matching something if it is not preceded by something else

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So with regex in java, I
want to write a regex that will match if and only if the pattern is not preceded by
certain characters. For
example:

String s = "foobar barbar
            beachbar crowbar bar
            ";

I want to match if
bar is not preceded by foo. So output would
be:

barbar
beachbar
crowbar

bar

I
know this is probably a very simple question. I am trying to learn regex, but in the
meantime I need something to work now.

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class="normal">Answer

You want
to use negative lookbehind like this:

\w*(?

Where
(? means "only if it doesn't have "x" before this
point".

See href="http://www.regular-expressions.info/lookaround.html" rel="noreferrer">Regular
Expressions - Lookaround for more
information.

Edit:
added the \w* to capture the characters before (e.g.
"beach").