Convert List to comma delimited string

[Joe Gliniecki]

I'm converting some code to use some of the new features in Java 1.5. The old code looks something like this:

List<String> myList = new ArrayList<String>();
// Add items to List
String newString = "";
for (Iterator<String> it = myList.iterator() ; it.hasNext() ; ){
  newString += it.next();
  if (it.hasNext()) {
    newString += ", "; 
  }
}
 

Is there a similar way to do this in a foreach loop? I can't find anything to check whether the current item in the foreach loop is the last one.

The only way I see to do it is either with the Iterator above, or with a foreach and getting rid of the comma at the end of the string after you exit the loop.

I know this isn't an earth shattering question, but curious if I'm missing another way to do this using foreach.

Thanks,
Joe

[Jeanne Boyarsky]

I can think of two ways:
1) Use a boolean to check if you are in the first iteration of the loop.
2) Always add the delimiter and then do a substring at the end to get rid of the last one.

[Mike Simmons]

I use something like this:

public static String join(Iterable<?> elements, String delimiter) {
  StringBuilder sb = new StringBuilder();
  for (Object e : elements) {
    if (sb.size() > 0)
      sb.append(delimiter); 
    sb.append(e);
  }
  return sb.toString();
}

[Rob Spoor]

And Mike's code also included another good advice: use StringBuilder instead of String for all the adding.

Everytime you concatenate Strings using +, a new StringBuilder object will be created. For example,

newString += it.next();

will be turned into

newString = new StringBuilder(newString).append(it.next()).toString();

By specifically using a StringBuilder, you'll make sure there is only one StringBuilder object instead of one per iteration.