Java regex Lookaround

see: http://www.rexegg.com/regex-lookarounds.html
Four ways of using lookarounds:

(?= lookahead

(?=\d{3} dollars).{3}

(Lookahead). Looks ahead for three digits followed by " dollars". Matches "100" in "100 dollars"

(?! negative lookahead

(?!=\d{3} pesos)\d{3}

(Negative Lookahead). Makes sure what follows is not three digits followed by " pesos". Matches "100" in "100 dollars"

(?<= lookbehind

(?<=USD)\d{3}

(Lookbehind). Makes sure "USD" precedes the text to be matched. Matches "100" in "USD100"

(?<! negative lookbehind

(?<!USD)\d{3}

(Negative Lookbehind). Makes sure "USD" does not precede the text to be matched. Matches "100" in "JPY100"

Lookaround after match:

\d{3}(?= dollars)

(Lookahead). Makes sure " dollars" follows the three digits to be matched. Matches "100" in "100 dollars"

\d{3}(?! dollars)

(Negative Lookahead) Makes sure " dollars" does not follow the three digits to be matched. Matches "100" in "100 pesos"

.{3}(?<=USD\d{3})

(Lookbehind). Looks behind for "USD" followed by three digits. Matches "100" in "USD100"

\d{3}(?<!USD\d{3})

(Negative Lookbehind). Makes sure what precedes is not "USD" followed by three digits. Matches "100" in "JPY100"

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