Question

e.g.:

• If the number is 234, I would like the result to be List<String> containing 2,3,4 (3 elements)
• If the number is 8763, I would like the result to be List<String> containing 8,7,6,3 (4 elements)

Does commons-math already have such a function?

Answer 1

1. Convert the number to a String (123 becomes "123"). Use Integer.toString.
2. Convert the string to a char array ("123" becomes {'1', '2', '3'}). Use String.toCharArray.
3. Construct a new, empty Vector<String> (or some other List type).
4. Convert each char in the char array to a String and push it onto the Vector ({'1', '2', '3'} becomes a Vector with "1", "2" and "3"). Use a for loop, Character.toString and List.add.

Edit: You can’t use the Vector constructor; have to do it manually.

int num = 123;
char[] chars = Integer.toString(num).toCharArray();
List<String> parts = new Vector<String>();
for (char c : chars)
{
    parts.add(Character.toString(c));
}

There isn’t an easier way to do this because it really isn’t a very obvious or common thing to want to do. For one thing, why do you need a List of Strings? Can you just have a list of Characters? That would eliminate step 3. Secondly, does it have to be a List or can it just be an array? That would eliminate step 4.