Scala Snippet as Java -

i'm working way through scala project, , converting java. everythings going fine, i'm stumbled snippet:

    pattern filenamepattern = pattern.compile("^(\\w+).*(_\\w+\\.xml)$");       new file(filepath).getname match {         case filenamepattern(first, last) => return first + last         case n => return n     } 

i understand regex, 1 or more letters, numbers or punctuation, followed 0 or more characters, followed 1 or more letters, numbers or punctuation. purpose of function file name file path, straight forward in java, have thought scala developer wouldn't make needlessly complex.

the problem is, don't want march ahead , assume developer idiot, when maybe they're trying little more clever, , lack of experience scala stopping me seeing it. please explain:

• the syntax match
• where hell first , last came from
• the equivalent / documentation leads java equivalent of snippet

def getfilename(filepath: string): string = {      if(filepath == null || filepath.trim.length == 0) {       return filepath     }      val filenamepattern = new regex("^(\\w+).*(_\\w+\\.xml)$")      new file(filepath).getname match {          case filenamepattern(first, last) => return first + last          case n => return n     } } 

the match construct used pattern matching. basically, left-hand side of match object match against patterns present in right-hand side. generated code tests each pattern in order appear, , if pattern matches object, code after => executed.

the first , last variables in match expression variables bound pattern matching machinery, when pattern, appear in, matches object. values corresponding value in object graph being matched. in other word, implicitly declared pattern, , initialized in "consequence" clause after =>.

classic example:

trait expr  case class const(val value: int) extends expr case class add(val left: expr, val right: expr) extends expr  def evaluate(exp: expr): int = exp match {     case const(cv) => cv     case add(exp1, exp2) => evaluate(exp1) + evaluate(exp2)     case _ => throw new illegalargumentexception("did not understand: " + exp) } 

scala's regular expression objects have provide special support pattern matching (via unapply/unapplyseq method). in case, if regular expression matches against string returned getname, variables first , last bound substring matching first subgroup of regular expression, , second subgroup respectively.

java has no match language construct. equivalent java code quite longish , troublesome. might like

final string name = (new file(filepath).getname()); final matcher matcher = filenamepattern.match(name);  if (matcher.matches()) {      final string first = matcher.group(1);     final string last = matcher.group(2);     return first + last;  } else {      return name; }