Java regex Lookaround

1. see: http://www.rexegg.com/regex-lookarounds.html
2. 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"
3. 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}(?<=USDd{3}) (Lookbehind). Looks behind for "USD" followed by three digits. Matches "100" in "USD100"
   •  d{3}(?<!USDd{3}) (Negative Lookbehind). Makes sure what precedes is not "USD" followed by three digits. Matches "100" in "JPY100"
4. n
5. n
6. n
7. n