for/in, more than anything else, is about convenience. However, with that convenience comes a degree of lost flexibility. One such example is the inability to determine the position in a list that the for/in construct resides at. As your code executes within the for/in loop, there is no way to access the position in the list. Additionally, the list variable itself isn't accessible, making its access equally impossible.
In short, you don't. Sometimes it's just as important to realize what you can't do as it is to learn what you can.
A common iteration technique is to use the loop variable, especially if it's numerical, in the loop body itself:
List<String> wordList = new LinkedList<String>( );
for (int i=0; i<args.length; i++) {
wordList.add("word " + (i+1) + ": '" + args[i] + "'");
}
This is perfectly legitimate, and really useful if you're performing some sort of count. However, it's impossible to access the iterator in a for/in loop, as that's kept internal (and not even generated until compilation takes place). In this case, you're out of luck. You can use for/in to display the results of a situation like this, but not to make the assignment itself:
public void determineListPosition(PrintStream out, String[] args)
throws IOException {
List<String> wordList = new LinkedList<String>( );
for (int i=0; i<args.length; i++) {
wordList.add("word " + (i+1) + ": '" + args[i] + "'");
}
for (String word : wordList) {
out.println(word);
}
}
This is hardly a severe limitation, but it's one you should be aware of.
Another common usage of lists is String concatenation, and that illustrates another of the for/in limitations. It's common in String concatenation to add separators between all but the last of a set of words, such as when printing a list. This separator is often a comma or perhaps a space:
StringBuffer longList = new StringBuffer( );
for (int i = 0, len=wordList.size( ); i < len; i++) {
if (i < (len-1)) {
longList.append(wordList.get(i))
.append(", ");
} else {
longList.append(wordList.get(i));
}
}
out.println(longList);
Here, all but the last word in the list has a comma appended to it, while the last one is appended without a comma. This makes for a nice list output. However, this rather simple task is impossible with for/in, because the variable that is used to do all the work, i, is inaccessible in a for/in loop. Again, a fairly minor inconvenience, but it's certainly not time to retire our old friend for just yet.