find the index of the longest string in an arraylist

[Ashley Feng]

i need to return the index of the longest string in the arraylist in java
so far i have

public static int findPosOfLargest(ArrayList<String> words) 
    {
        String largest = words.get(0);
        int x = 0;
        for(int i = 0; i < words.size(); i++)
        {
            if(words.get(i).length() > largest.length())
            {
                largest = words.get(i);
                x = i;
            }
        }
        return x;
    }

but all it does is return 0

[Vijay Vishwa]

Hi Ashley,
I see there is no problem in the code and logic. It works fine.
Can you first print the ArrayList and see what are the values inside. It may be that the First string is largest itself.

Here how I tested it.

import java.util.ArrayList;

public class LargestString {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub

		ArrayList<String> arr = new ArrayList<String>();
		arr.add("one");
		arr.add("five");
		arr.add("seven");
		System.out.println(findPosOfLargest(arr));
		
	}

	public static int findPosOfLargest(ArrayList<String> words)    
    {   
        String largest = words.get(0);   
        int x = 0;   
        for(int i = 0; i < words.size(); i++)   
        {   
            if(words.get(i).length() > largest.length())   
            {   
                largest = words.get(i);   
                x = i;   
            }   
        }   
        return x;   
    }  

}

Output is 2

[Winston Gutkowski]

Ashley Feng wrote:so far i have...

Like Vijay, I can't see anything logically wrong with your method, but it does contain a few possibilities for improvement:

1. I'd definitely get into the habit of using for-each loops for collections, because
(a) they usually have less boilerplate.
(b) they're less likely to be affected by the type of Collection they operate on.
For example, your method could be re-written:

public static int findPosOfLargest(List<String> words) {
   int max_length = -1;
   int longest = -1;
   int current = 0;
   for(String word: words) {
      int length = word.length();
      if(length > max_length) {
         max_length = length;
         longest = current;
      }
      ++current;
   }
   return longest;
}

and it will work just as fast whether your List is an ArrayList or a LinkedList (your loop won't).
Their main disadvantage is that you have to define the index outside the loop, but in this case I reckon it's probably worth it.

2. Prefer variables to method calls. Your loop has to call size() for each iteration, but

for(int i = 0, s = words.size(); i < s; i++) {
   ...
}

only calls it once. Now in this case it probably doesn't make a lot of difference, but it is worth remembering.

3. Cover all your bases. Your method silently returns a valid index (0) if the supplied List is empty, whereas the example above returns -1. An alternative is to throw an Exception, which is equally valid. Just remember to allow for it and document what happens.

HIH

Winston