[Ch15b] Replacing ChatHistory class with straight use of List.

public class LotsOfReaders {

  public static void main(String[] args) {

    ChatHistory chatHistory = new ChatHistory();

    List<Chat> chatHistory = new ArrayList<>();

    ExecutorService executor = Executors.newFixedThreadPool(3);

    for (int i = 0; i < 5; i++) {

      executor.execute(() -> chatHistory.add("Hi there!"));

      executor.execute(() -> chatHistory.add(new Chat("Hi there!")));

      executor.execute(() -> printChatHistory("Reader 1", chatHistory));

      executor.execute(() -> printChatHistory("Reader 2", chatHistory));

    }

    executor.shutdown();

  }

  private static void printChatHistory(String name, ChatHistory chatHistory) {

    for (Chat chat : chatHistory.getHistory()) {

  private static void printChatHistory(String name, List<Chat> chatHistory) {

    for (Chat chat : chatHistory) {

      System.out.println(name + " read: " + chat);

    }

  }

}

class ChatHistory {

  private final List<Chat> history = new ArrayList<>();

  public List<Chat> getHistory() {

    return history;

  }

  public void add(String message) {

    history.add(new Chat(message));

  }

}

class Chat {

  private final String message;

  private final LocalDateTime timestamp;

    timestamp = LocalDateTime.now();

  }

  @Override

  public String toString() {

    String time = timestamp.format(ofLocalizedTime(FormatStyle.MEDIUM));

    return time + " " + message;