如何防止用户在Hangman JAVA中输入相同的字母？

import java.util.HashSet;
import java.util.Scanner;
import java.util.Set;

public class HangmanGame {
    private Set<Character> guessedLetters;

    public HangmanGame() {
        guessedLetters = new HashSet<>();
    }

    public void play() {
        Scanner scanner = new Scanner(System.in);
        char guess;

        while (true) {
            System.out.print("Enter a letter: ");
            guess = scanner.next().charAt(0);

            if (guessedLetters.contains(guess)) {
                System.out.println("You have already guessed this letter. Please try again.");
                continue;
            }

            guessedLetters.add(guess);

            // 继续游戏逻辑...
        }
    }

    public static void main(String[] args) {
        HangmanGame game = new HangmanGame();
        game.play();
    }
}