Index of an ArrayList?

Of course the maximum is wordList.size(), this happens when all wordList's words are short words. Then, wordList from position 0 to position wordList.size() - 1 (both included) are short.

The maximum index of an array or ArrayList will be size-1. This is because the index of a collection is 0 based. You can think of the index as an offset.

Let's say I have an ArrayList with the following contents:

["abc"]

There is 1 element in the array, so its size is 1. The index (or offset) of the first element is 0 because it is at the root of the array. If my array is:

["abc", "bcd", "cde", "def" ]

Then you can see that there are 4 entries in the array, so the size is 4. The offset to the final element "def" is 3 because you have to take 3 steps forward from the root to get there. 0 steps gives you "abc", 1 step gives "bcd", 2 = "cde" and 3 = "def". So the size is 4 but you can't get the item at the 4th index because 4 steps takes you beyond "def".

for(String s : wordList)
   if(s.length() < 4)
     System.out.println("SHORT WORD");

basically says "Call the first word in the list s. If this word is less than 4 letters long, print "SHORT WORD" to the console. Now, repeat for the second word and so on until there are no words left."

Therefore, if all of the words in the list were less than 4 letters long, "SHORT WORD" would be printed wordlist.size() times.

You ask:

"What is the maximum number of times SHORT WORD can be printed?"

If all items of wordList have length < 4, then all items will be printed.

So, how many itens does wordList have? Simple: wordList.size().

ArrayList's size() method semantic:

In a ArrayList with a total of 3 itens, such as:

ArrayList wordList = new ArrayList<String>();
wordList.add("firstWord");
wordList.add("2ndWrd");
wordList.add("3w");

The size() is the number of items (like array.length). So, in this case, 3.

But ArrayList's index, as a regular array, is 0-based (going from 0 to size()-1). So:

wordList.get(0); // returns "firstWord"
wordList.get(1); // returns "2ndWrd"
wordList.get(2); // returns "3w"
wordList.get(3); // throws an exception (IndexOutOfBoundsException)

Thus your confusion.

Infinetely many times. word list is declared as ArrayList, but it can actually be subclass of array list. Thus you can make array list that returns infinite iterator returning empty strings.

ArrayList<String> wordList = new ArrayList<String>() {
        @Override
        public Iterator<String> iterator() {
            return new Iterator<String>() {
                @Override
                public boolean hasNext() {
                    return true;
                }

                @Override
                public String next() {
                    return "";
                }

                @Override
                public void remove() {
                    throw new UnsupportedOperationException("Not supported yet.");
                }
            };
        }
    };
    for (String s : wordList) {
        if (s.length() < 4) {
            System.out.println("SHORT WORD");
        }
    }