String Manipulation Tricks (Day 1)

private static final Pattern THE_NUMBER =    Pattern.compile("^\\s\\(([1-9][0-9]*)\\)$");// Find the number from string with header.// example: parseTheNumber("foo", "foo (123)") -> 123//          parseTheNumber("foo", "bar (123)") -> empty//          parseTheNumber("foo", "foo (str)") -> emptyOptional<Integer> parseTheNumber(String header, String string) {  if (!string.startsWith(header)) {    return Optional.empty();  }  Matcher matcher = THE_NUMBER.matcher(      string.substring(header.length()));  try {    return matcher.matches()        ? Optional.of(Integer.parseInt(matcher.group(1)))        : Optional.empty();  } catch (NumberFormatException e) {    return Optional.empty();  }}

import com.google.common.primitives.Ints;import com.google.mu.util.StringFormat;private static final StringFormat THE_NUMBER =    new StringFormat("{header} ({num})");Optional<Integer> parseTheNumber(String header, String string) {  // StringFormat.parse() will return empty()  //     if failed to parse, or if the lambda returns null  return THE_NUMBER.parse(      string,      // Ints.tryParse() returns null if failed to parse      (h, num) -> h.equals(header) ? Ints.tryParse(num) : null);}