https://qiita.com/haraitai/items/cb668d31c4127fcd6f5a#comment-9c876c55d8e3e7b9ce0a

BlackJack.java

import java.util.ArrayList;
import java.util.List;
import java.util.Collections;
import java.util.stream.Collectors;
import java.util.Scanner;

public class BlackJack {
    public static void main(String[] args) {
        System.out.println("ブラックジャックゲーム");
        Deck deck = new Deck();
        Dealer dealer = new Dealer();
        Player player = Human.create();
        dealer.deal(deck, player);
    }
}

abstract class Player {
    protected final String name;
    protected final List<Card> cards;

    public Player(String name) {
        this.name = name;
        this.cards = new ArrayList<>();
    }

    public void hold(Card card) {
        cards.add(card);
    }

    public abstract boolean hit();

    public int score() {
        int score = cards.stream().mapToInt(card -> Math.min(card.rank.number, 10)).sum();
        return score <= 11 && hasAce() ? score + 10 : score;
    }

    private boolean hasAce() {
        return cards.stream()
                    .filter(card -> card.isAce())
                    .findFirst()
                    .isPresent();
    }

    public boolean isBust() {
        return score() > 21;
    }

    public boolean isStrongerThan(Player other) {
        return !isBust() && (other.isBust() || score() > other.score());
    }

    public void showCards() {
        System.out.println(name + "の手:" +
                           cards.stream()
                                .map(card -> card.toString())
                                .collect(Collectors.joining("、")));
        System.out.println(name + "の点数: " + score());
    }
}

class Human extends Player {
    private static final Scanner scanner = new Scanner(System.in);

    public Human(String name) {
        super(name);
    }

    public static Human create() {
        System.out.print("名前を入力してください > ");
        return new Human(scanner.nextLine());
    }

    @Override
    public boolean hit() {
        showCards();
        while (isBust()) {
            return false;
        }
        System.out.print("もう一枚挽くなら y 、ひかないなら n を入力してください > ");
        while (true) {
            String line = scanner.nextLine();
            if (line.equals("y")) {
                return true;
            } else if (line.equals("n")) {
                return false;
            }
            System.out.println("y か n を入力してください");
        }
    }
}

class Dealer extends Player {

    public Dealer() {
        super("ディーラー");
    }

    public boolean hit() {
        showCards();
        return score() < 17;            // 合計点が17未満ならカードが欲しい
    }

    public void deal(Deck deck, Player player) {
        player.hold(deck.draw());
        player.hold(deck.draw());
        this.hold(deck.draw());
        this.hold(deck.draw());
        System.out.println(name + "のカード1枚目: " + cards.get(0));

        while (player.hit()) {
            player.hold(deck.draw());
        }
        while (this.hit()) {
            this.hold(deck.draw());
        }

        judge(player);
    }

    private void judge(Player player) {
        if (this.isStrongerThan(player)) {
            System.out.println(this.name + "の勝ちです！");
        } else if (player.isStrongerThan(this)) {
            System.out.println(player.name + "の勝ちです！");
        } else {
            System.out.println("引き分けです。");
        }
    }
}

class Deck {
    private final List<Card> cards = new ArrayList<>();

    public Deck() {
        for (Suit suit: Suit.values()) {
            for (int number = 1; number <= 13; number++) {
                cards.add(new Card(suit, new Rank(number)));
            }
        }
        Collections.shuffle(cards);
    }

    public Card draw() {
        return cards.remove(0);
    }
}

class Card {
    public final Suit suit;
    public final Rank rank;
    public final String label;

    public Card(Suit suit, Rank rank) {
        this.suit = suit;
        this.rank = rank;
        this.label = suit.label + "の" + rank.label;
    }

    @Override
    public String toString() {
        return this.label;
    }

    boolean isAce() {
        return this.rank.label.equals("A");
    }
}

enum Suit {
    SPADE("スペード"),
    HEART("ハート"),
    DIAMOND("ダイヤ"),
    CLUB("クラブ");

    public final String label;

    Suit(final String label) {
        this.label = label;
    }
}

class Rank {
    public static final String[] LABELS = {
        "?", "A", "2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K"
    };

    public final int number;
    public final String label;

    Rank(int number) {
        if (number < 1 || number > 13) {
            throw new IllegalArgumentException();
        }
        this.number = number;
        this.label = LABELS[number];
    }
}