java - To compile or not to compile the pattern? -

i'm working on script code generator. created template script file, contains place holders few parameters , placeholders, should replaced real values during generation. replacement performed within loop(s). performance of generator kind of important (currently on java 7). dilemma follows:

do this:

private final string pholder_sect = "#__phold_sect__#"; private final string param_pid    = "__param_pid"; private final string param_name   = "__param_name"; private final string param_desc   = "__param_desc"; ... (int = 0; < sectioncount; i++) {      // here...     mastertmpl[i] = mastertmpl[i].replace(pholder_sect, somesectioncode);     // else here...     mastertmpl[i] = mastertmpl[i].replace(param_desc, desc)                                  .replace(param_name, name)                                  .replace(param_pid,  pid)     ... } 

or (the point being placeholders complied patterns):

private final pattern regexsect = pattern.compile("#__phold_sect__#", pattern.literal); private final pattern regexpid  = pattern.compile("__param_pid",      pattern.literal); private final pattern regexname = pattern.compile("__param_name",     pattern.literal); private final pattern regexdesc = pattern.compile("__param_desc",     pattern.literal); ... (int = 0; < sectioncount; i++) {      // here...     mastertmpl[i] = this.regexsect.matcher(mastertmpl[i]).replaceall(matcher.quotereplacement(somesectioncode));     // else here...     mastertmpl[i] = this.regexdesc.matcher(mastertmpl[i]).replaceall(matcher.quotereplacement(desc));     mastertmpl[i] = this.regexname.matcher(mastertmpl[i]).replaceall(matcher.quotereplacement(name));     ... } 

i know can measure execution, , stuff, i'm kind of hoping answer explains (un)importance of pattern compilation in particular case...

this code faster, finds occurrences of patterns in single search (instead of 1 per pattern); , importantly, replacements in single pass, instead of requiring 1 pass per pattern. building many strings expensive, because of copying , memory overhead - builds 1 fully-replaced string, in last line.

    public static string replacemany(string input,              map<string, string> replacements) {         // build composite pattern replacement keys         stringbuilder sb = new stringbuilder();         string prefix = "";         (string k : replacements.keyset()) {             sb.append(prefix).append(pattern.quote(k));             prefix = "|";         }         pattern p = pattern.compile(sb.tostring());         // replace in single loop         matcher m = p.matcher(input);         stringbuffer output = new stringbuffer();         while (m.find()) {             // inspired http://stackoverflow.com/a/948381/15472             m.appendreplacement(output, "");             output.append(replacements.get(m.group(0)));         }         m.appendtail(output);         return output.tostring();     }