Find the Longest and the Shortest Words in a Sentence in Java

Write a Java Program to input a sentence and find and display the longest and the shortest words from that sentence along with their lengths.

import java.util.Scanner;
class Find{
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        System.out.print("Sentence: ");
        String s = in.nextLine().trim().toUpperCase();
        char last = s.charAt(s.length() - 1);
        if(".!?".indexOf(last) == -1){
            System.out.println("Invalid sentence!");
            return;
        }
        String word = new String();
        String longest = new String();
        String shortest = new String(s);
        for(int i = 0; i < s.length(); i++){
            char ch = s.charAt(i);
            if(Character.isLetterOrDigit(ch))
                word += ch;
            else{
                if(longest.length() < word.length())
                    longest = new String(word);
                if(shortest.length() > word.length())
                    shortest = new String(word);
                word = new String();
            }
        }
        System.out.println("Longest word: " + longest);
        System.out.println("Length of the longest word: " + longest.length());
        System.out.println("Shortest word: " + shortest);
        System.out.println("Length of the smallest word: " + shortest.length());
    }
}