Indexing an array list

I have an arraylist like this in Java with around 242 elements in it.

ArrayList<String> AL=new ArrayList<>();

AL.add("Apple");
AL.add("Banana");
AL.add("BArbie");
AL.add("Elephant");
AL.add("Zombie");
and so on...

Once the values are inserted, i sort using

Collections.sort(AL);

Now i want to create an index for this ArrayList based on the first character. In the above example, if i want to locate Z, it would be position 5 and so on. If y is selected, then the nearest previous value to be given , in this case it is Elephant.

This solution is achieved currently by processing the data using 2 database tables and java processing. any suggestions on how to minimize the complexity.

If we get direction on how to get to an alternate solution, we would be really happy.

Thanks.

1. I think you use incorrect Collection. In case you do not have duplicates - then do use TreeSet, otherwise - PriorityQueue. These collections have internal sortings.
2. As I understand you add new elements and want to retreive new index. Why do not you use Map<Character, Set<String>> instead?!

To make it more vivid let's assume you have a list of countries. Arrays.asList("Afghanistan", "Albania", "Eritrea", ...) You could create a map TreeMap<Character,List<String>> out of your list with first char as key and a list of strings which starts with the key as value.

I intentionally suggest treemap here because the functionality you want is already implemented in the methods floorEntry() and floorKey().

The following example should give you a starting point:

import java.util.Arrays;
import java.util.List;
import java.util.TreeMap;
import java.util.stream.Collectors;

public class Test {

    public static void main(String[] args) throws Exception {
        List<String> countries = Arrays.asList("Afghanistan", "Albania", "Algeria",
                                                "Bahamas", "Bahrain", "Bangladesh",
                                                "Cameroon", "Canada", "Central African Republic",
                                                "Eritrea", "Estonia", "Ethiopia",
                                                "Nigeria", "North Korea", "Norway",
                                                "Sweden", "Switzerland", "Syria",
                                                "Uganda", "Ukraine", "United Kingdom",
                                                "Venezuela", 
                                                "Yemen",
                                                "Zimbabwe");

        TreeMap<Character,List<String>> map = countries.stream()
                .collect(Collectors.groupingBy(s -> s.charAt(0), TreeMap::new, Collectors.toList()));
        
        System.out.println(map.floorEntry('F').getValue().get(0));
    }
}