Initials in Java

Given a person's full name fullName, made of a first name and a last name, return their initials: the first letter of each name, in upper case.

The two names are separated by a single space. The initials are always upper case, even when the name is written in lower case.

Example 1:

Input: fullName = "grace hopper"
Output: "GH"
Explanation: The first name starts with g and the last name with h. In upper case, they give "GH".

Example 2:

Input: fullName = "Ada Lovelace"
Output: "AL"
Explanation: A and L are already upper case, so they stay as they are.

Example 3:

Input: fullName = "a b"
Output: "AB"
Explanation: A name can be a single letter: that letter is its initial.

Constraints:

• fullName has exactly two words, the first name and the last name, separated by one space.
• Both names are made of English letters only, lower case or upper case.