Detecting the first iteration through a for-each loop in Java

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.