CODEWITHSUNDEEP
javaiteratorforeach
cometta
cometta

Reputation: 35689

Java foreach loop: for (Integer i : list) { ... }

When I use JDK5 like below

ArrayList<Integer> list = new ArrayList<Integer>();  
     for (Integer i : list) { 

      //cannot check if already reached last item

   }

on the other hand if I just use an Iterator

ArrayList<Integer> list = new ArrayList<Integer>();
  for (Iterator i = list.iterator(); i.hasNext();) {

          //i can check whether this is last item
          if(i.hasNextItem()){
          }

    }

How can I check if I've already reached last item with for (Integer i : list) {

Upvotes: 20

Views: 194245

Answers (4)

Thomas Jung
Thomas Jung

Reputation: 33092

The API does not support that directly. You can use the for(int i..) loop and count the elements or use subLists(0, size - 1) and handle the last element explicitly:

  if(x.isEmpty()) return;
  int last = x.size() - 1;
  for(Integer i : x.subList(0, last)) out.println(i);
  out.println("last " + x.get(last));

This is only useful if it does not introduce redundancy. It performs better than the counting version (after the subList overhead is amortized). (Just in case you cared after the boxing anyway).

Upvotes: 4

Romain Linsolas
Romain Linsolas

Reputation: 81617

One way to do that is to use a counter:

ArrayList<Integer> list = new ArrayList<Integer>();
...
int size = list.size();
for (Integer i : list) { 
    ...
    if (--size == 0) {
        // Last item.
        ...
    }
}

Edit

Anyway, as Tom Hawtin said, it is sometimes better to use the "old" syntax when you need to get the current index information, by using a for loop or the iterator, as everything you win when using the Java5 syntax will be lost in the loop itself...

for (int i = 0; i < list.size(); i++) {
    ...

    if (i == (list.size() - 1)) {
        // Last item...
    }
}

or 

for (Iterator it = list.iterator(); it.hasNext(); ) {
    ...

    if (!it.hasNext()) {
        // Last item...
    }
}

Upvotes: 36

Esko
Esko

Reputation: 29367

Another way, you can use a pass-through object to capture the last value and then do something with it:

List<Integer> list = new ArrayList<Integer>();
Integer lastValue = null;
for (Integer i : list) {
    // do stuff
    lastValue = i;
}
// do stuff with last value

Upvotes: 3

Tom Hawtin - tackline
Tom Hawtin - tackline

Reputation: 147154

Sometimes it's just better to use an iterator.

(Allegedly, "85%" of the requests for an index in the posh for loop is for implementing a String join method (which you can easily do without).)

Upvotes: 9

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