Find Frequency of each alphabet present

AlphabetFrequency.java

/*
Accept a senetnce and print the frequency of each alphabet present

INPUT:  Smooth Road
OUTPUT:
    s: 1
    m: 1
    o: 3
    t: 1
    h: 1
    r: 1
    a: 1
    d: 1
*/

import java.util.Scanner;

class AlphabetFrequency {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter a sentence");
        String sen = sc.nextLine();

        String sentence = "";

        for (int i = 0; i < sen.length(); i++)
            if (sen.charAt(i) != ' ')
                sentence += sen.charAt(i);

        sentence = sentence.toLowerCase();

        int alphabets[] = new int[26];

        for (int i = 0; i < sentence.length(); i++) {
            int index = sentence.charAt(i) - 'a';
            alphabets[index]++;
        }

        for (int i = 0; i < 26; i++) {
            if (alphabets[i] != 0) {
                System.out.println((char) (i + 'a') + ": " + alphabets[i]);
            }
        }
    }
}