java program to separate alphabets and numbers from string

package com.usr.strings;

public class SeparateAlphabetsAndDigitsFromString {

       public static void main(String[] args) {

              String input = "1a2b3c4defgh567jkl";

              separateDigitsAndAlphabets(input);

       }

       public static void separateDigitsAndAlphabets(String str) {

              String number = "";

              String letter = "";

              for (int i = 0; i < str.length(); i++) {

                     char a = str.charAt(i);

                     if (Character.isDigit(a)) {

                           number = number + a;

                     } else {

                           letter = letter + a;

                     }

              }

              System.out.println("Alphates in string:"+letter);

              System.out.println("Numbers in String:"+number);

       }

}

output 

Alphates in string:abcdefghjkl
Numbers in String:1234567