Split a alphabetically sorted list into sublists based on alphabets in java

Question

I have a sorted list in java, i just want to split this list into sublists based on the first alphabet at each index of list. For example List contains

{
calculator,
catch,
doll,
elephant
}

i want the sublists as

{calculator,catch}
{doll}
{elephant}

I dont want to put 26 if statements, is there any efficient and correct way of doing this. The list is already sorted alphabetically. Any help will be highly appreciated.

Answer 1

You could use Java 8 Streams. Unfortunately, this method doesn't take advantage from the list being sorted already. list has to be the list containing your elements.

Map<Character, List<String>> collect =
        list.stream().collect(Collectors.groupingBy(elem -> elem.charAt(0)));

Answer 2

The solution of @SilverNak is good with Java-8, you can use this also if you are not using Java-8 :

public static void main(String[] args) {
    String list[] = {"calculator", "catch", "doll", "elephant"};
    Map<Character, List<String>> map = new HashMap<>();

    List<String> lst;
    for (String str : list) {
        //if the key exit then add str to your list else add a new element
        if (map.containsKey(str.charAt(0))) {
            map.get(str.charAt(0)).add(str);
        } else {
            lst = new ArrayList<>();
            lst.add(str);
            map.put(str.charAt(0), lst);
        }
    }
}