Here's an example of a program in Java that swaps the first and last characters of each word in a sentence 

import java.util.Scanner;

public class SwapCharacters {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter a sentence: ");
        String sentence = sc.nextLine();

        String[] words = sentence.split(" ");

        for (int i = 0; i < words.length; i++) {
            char[] wordChars = words[i].toCharArray();
            int length = wordChars.length;
            char first = wordChars[0];
            char last = wordChars[length - 1];

            wordChars[0] = last;
            wordChars[length - 1] = first;

            words[i] = new String(wordChars);
        }

        String result = String.join(" ", words);
        System.out.println("Result: " + result);
    }
}

This program uses a Scanner object to take an input sentence from the user. It then splits the sentence into words using the split() method and stores the words in a String array.

For each word in the array, the program converts it into a char array and swaps the first and last characters. Finally, the program joins the words back into a sentence using the String.join() method and prints the result