Last iteration of enhanced for loop in java

Is there a way to determine if the loop is iterating for the last time. My code looks something like this:

int[] array = {1, 2, 3...};
StringBuilder builder = new StringBuilder();

for(int i : array)
{
    builder.append("" + i);
    if(!lastiteration)
        builder.append(",");
}

Now the thing is I don't want to append the comma in the last iteration. Now is there a way to determine if it is the last iteration or am I stuck with the for loop or using an external counter to keep track.

Solution 1:

Another alternative is to append the comma before you append i, just not on the first iteration. (Please don't use "" + i, by the way - you don't really want concatenation here, and StringBuilder has a perfectly good append(int) overload.)

int[] array = {1, 2, 3...};
StringBuilder builder = new StringBuilder();

for (int i : array) {
    if (builder.length() != 0) {
        builder.append(",");
    }
    builder.append(i);
}

The nice thing about this is that it will work with any Iterable - you can't always index things. (The "add the comma and then remove it at the end" is a nice suggestion when you're really using StringBuilder - but it doesn't work for things like writing to streams. It's possibly the best approach for this exact problem though.)

Solution 2:

Another way to do this:

String delim = "";
for (int i : ints) {
    sb.append(delim).append(i);
    delim = ",";
}

Update: For Java 8, you now have Collectors

Solution 3:

It might be easier to always append. And then, when you're done with your loop, just remove the final character. Tons less conditionals that way too.

You can use StringBuilder's deleteCharAt(int index) with index being length() - 1

Solution 4:

Maybe you are using the wrong tool for the Job.

This is more manual than what you are doing but it's in a way more elegant if not a bit "old school"

 StringBuffer buffer = new StringBuffer();
 Iterator iter = s.iterator();
 while (iter.hasNext()) {
      buffer.append(iter.next());
      if (iter.hasNext()) {
            buffer.append(delimiter);
      }
 }