question: public static boolean isPossibleRegex ( String str ) { for ( int i = 0 ; i < str . length ( ) ; i ++ ) { switch ( str . charAt ( i ) ) { case '*' : return true ; case '{' : if ( i < str . length ( ) - 1 && str . charAt ( i + 1 ) != '}' ) return true ; break ; case '|' : return true ; case '?' : if ( i > 1 && str . charAt ( i - 1 ) == ')' ) return true ; break ; default : break ; } } return false ; }
target:  Checks whether the string could possibly represent a regular expression (this is just a first, fast guess, which will need to be verified by actually constructing the regex using the constructRegex method below).