Write a Java program to enter any sentence and convert the sentence to uppercase. Print only those words of the sentence whose first and last letters are the same.

import java.util.Scanner;

public class KboatString
{
    public static void main(String args[]) {
        Scanner in = new Scanner(System.in);
        System.out.println("Enter a sentence: ");
        String str = in.nextLine();
        str = str.toUpperCase();
        str += " ";
        int len = str.length();
        String word = "";
        
        for (int i = 0; i < len; i++) {
            char ch = str.charAt(i);
            if (ch == ' ') {
                char first = word.charAt(0);
                char last = word.charAt(word.length() - 1);
                if (first == last) {
                    System.out.println(word);
                }
                
                word = "";
            }
            else {
                word += ch;
            }
        }
    }
}