Question

I’m working on a server that returns character separated lists to its client.
In order to build these lists I have to detect the first iteration through a for-each loop:

    StringBuilder builder = new StringBuilder() ;
    boolean firstIterationFlag = true ;

    for ( String s : list ){
        if ( firstIterationFlag) {
            firstIterationFlag = false ;
        } else {
            builder.append(separator);
        }
        builder.append(s) ;         
   }
   return builder.toString() ;

Is there a way of doing this without the flag?

Answer 1

One simpler way for this situation is to note that you can always append an empty string:

// For the first iteration, use a no-op separator
String currentSeparator = "";
for (String s : list) {
    builder.append(currentSeparator);
    builder.append(s);
    // From the second iteration onwards, use this
    currentSeparator = separator;
}

Alternatively (and preferrably) use Guava’s Joiner class to start with 🙂

This “joiner” scenario is almost always the one given for this requirement – so just use Joiner. For other scenarios, either use a regular for loop or use the condition as per your code.