Capitalize First and Last character of String

CaptializeChar.Java

package javaproblems;

public class CaptializeChar {
    
    public static String getCaptilizeString(String words){
        if(words.length()<=0){
            return "Invalid String";
        }
        
        String[] splitWords = words.split("\\ ");
        StringBuilder returnStr = new StringBuilder(words.length());
        for(int i =0; i <splitWords.length; i++){
            String firstChar = String.valueOf(Character.toUpperCase(splitWords[i].charAt(0)));
            String btwn = splitWords[i].substring(1, splitWords[i].length()-1);
            String lastChar = String.valueOf(Character.toUpperCase(splitWords[i].charAt(splitWords[i].length()-1)));
            returnStr.append(firstChar).append(btwn).append(lastChar).append(" ");
        }
        return returnStr.toString();
    }
    
    public static void main(String[] args){
        System.out.println(getCaptilizeString("hello world how are you"));
    }
}