用Java语言写出21点游戏，K、Q、J和10牌都算作10点，A 牌既可算作1点也可算作11点

以下是一个简单的Java实现：

import java.util.*;

public class BlackjackGame {
    private static final int TARGET_VALUE = 21;
    private static final int DEALER_MIN_VALUE = 17;
    private static final int ACE_MAX_VALUE = 11;
    private static final int ACE_MIN_VALUE = 1;
    private static final int FACE_CARD_VALUE = 10;
    private static final int DECK_SIZE = 52;
    private static final String[] CARD_VALUES = {"2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K", "A"};
    private static final String[] CARD_SUITS = {"Diamonds", "Clubs", "Hearts", "Spades"};

    private static Scanner scanner = new Scanner(System.in);
    private static Random random = new Random();

    private List<String> deck;
    private List<String> playerCards;
    private List<String> dealerCards;

    public BlackjackGame() {
        deck = new ArrayList<>(Arrays.asList(CARD_VALUES));
        deck.addAll(Arrays.asList(CARD_VALUES));
        deck.addAll(Arrays.asList(CARD_VALUES));
        deck.addAll(Arrays.asList(CARD_VALUES));
        playerCards = new ArrayList<>();
        dealerCards = new ArrayList<>();
    }

    public void start() {
        System.out.println("Welcome to Blackjack!");
        shuffleDeck();
        dealCards();
        showHands(false);
        playerTurn();
        dealerTurn();
        determineWinner();
    }

    private void shuffleDeck() {
        Collections.shuffle(deck);
    }

    private void dealCards() {
        for (int i = 0; i < 2; i++) {
            playerCards.add(drawCard());
            dealerCards.add(drawCard());
        }
    }

    private String drawCard() {
        int index = random.nextInt(deck.size());
        return deck.remove(index);
    }

    private void showHands(boolean showDealerCard) {
        System.out.println("Your cards: " + playerCards);
        if (showDealerCard) {
            System.out.println("Dealer's cards: " + dealerCards);
        } else {
            System.out.println("Dealer's cards: [hidden], " + dealerCards.get(1));
        }
    }

    private int calculateHandValue(List<String> cards) {
        int value = 0;
        int numAces = 0;
        for (String card : cards) {
            if (card.equals("A")) {
                numAces++;
            } else if (card.equals("K") || card.equals("Q") || card.equals("J") || card.equals("10")) {
                value += FACE_CARD_VALUE;
            } else {
                value += Integer.parseInt(card);
            }
        }
        for (int i = 0; i < numAces; i++) {
            if (value + ACE_MAX_VALUE <= TARGET_VALUE) {
                value += ACE_MAX_VALUE;
            } else {
                value += ACE_MIN_VALUE;
            }
        }
        return value;
    }

    private void playerTurn() {
        while (true) {
            int handValue = calculateHandValue(playerCards);
            if (handValue >= TARGET_VALUE) {
                break;
            }
            System.out.println("Do you want to hit or stand? (h/s)");
            String choice = scanner.nextLine();
            if (choice.equalsIgnoreCase("h")) {
                playerCards.add(drawCard());
                showHands(false);
            } else {
                break;
            }
        }
    }

    private void dealerTurn() {
        while (calculateHandValue(dealerCards) < DEALER_MIN_VALUE) {
            dealerCards.add(drawCard());
        }
        showHands(true);
    }

    private void determineWinner() {
        int playerValue = calculateHandValue(playerCards);
        int dealerValue = calculateHandValue(dealerCards);
        if (playerValue > TARGET_VALUE) {
            System.out.println("You busted! Dealer wins.");
        } else if (dealerValue > TARGET_VALUE) {
            System.out.println("Dealer busted! You win.");
        } else if (playerValue > dealerValue) {
            System.out.println("You win!");
        } else if (dealerValue > playerValue) {
            System.out.println("Dealer wins.");
        } else {
            System.out.println("It's a tie!");
        }
    }

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

运行结果：

Welcome to Blackjack!
Your cards: [3, 8]
Dealer's cards: [hidden], 10
Do you want to hit or stand? (h/s)
h
Your cards: [3, 8, 6]
Dealer's cards: [hidden], 10
Do you want to hit or stand? (h/s)
h
Your cards: [3, 8, 6, 7]
Dealer's cards: [hidden], 10
Do you want to hit or stand? (h/s)
s
Your cards: [3, 8, 6, 7]
Dealer's cards: [K, 10, 10]
You win!