public class MyRunnable implements Runnable {
    public void run(){
        System.out.println("MyRunnable running");
    }
}

Thread thread = new Thread(new MyRunnable());
thread.start();

Implements Runnable

Runnable runnable = new Runnable(){
    public void run(){
        System.out.println("MyRunnable running");
    }
};

Thread thread = new Thread(runnable);
thread.start();

Anonymous Implementation of Runnable

Runnable runnable = new Runnable(){
    public void run(){
        System.out.println("MyRunnable running");
    }
};

public class MyRunnable implements Runnable {
    public void run(){
        System.out.println("MyRunnable running");
    }
}

Runnable myRunnable = () -> System.out.println("MyRunnable running");

Thread thread = new Thread(myRunnable);
thread.start();

Lambda implementation

@FunctionalInterface

interface Function<T, R>

interface Supplier<T>
interface Consumer<T>

interface Predicate<T>

...

@FunctionalInterface
interface Callback {
    void call(String response);
}

public static void search(String term, Callback callback) {
    // make async call when it returns run callback
    // function with response
    // {...}
    //

    callback.call(term + " found");
}

@FunctionalInterface

users.stream().filter((User user) -> user.gender == Gender.MALE)
              .map((User user) -> user.cardLimit)
              .reduce((v1, v2) -> v1 + v2)
              .get()

@FunctionalInterface

public static int sum(int a, int b) {
    return a + b;
}

Pure function

public static int subtract(int a, int b) {
    return new Random().nextInt() - a - b;
}

public static int multiply(int a, int b) {
    int result = a * b;

    OtherClass.persist(result);

    return result;
} // With side effects

Impure function

"FUNCTIONS SHOULD DO ONE THING. THEY SHOULD DO IT WELL. THEY SHOULD DO IT ONLY"

Robert C. Martin Clean Code

@Override
public UserCardResponse getCardById(UUID userId, UUID cardId, String expand) {
  // verifica se o usuario existe e nao esta com o status igual a DELETADO.
  UserDomain userDomain = userService.getById(userId);
  if (userDomain == null) {
    throw new NotFoundException(this.messageError.create(Messages.USER_NOT_FOUND));
  }
  // verifica se o card existe
  Integer positionCard = this.positionCard(userDomain.getCard(), cardId);
  if (positionCard < 0) {
    throw new NotFoundException(this.messageError.create(Messages.CARD_NOT_FOUND));
  }
  CardDomain cardDomain = userDomain.getCard().get(positionCard);
  if (ObjectUtils.isEmpty(cardDomain)) {
    throw new NotFoundException(this.messageError.create(Messages.CARD_NOT_FOUND));
  }
  ...

  if (!ObjectUtils.isEmpty(cardDomain.getNumberBin())) {
    Optional<BinDomain> binDomain = this.binRepository.findById(cardDomain.getNumberBin());
    binDomain.ifPresent(cardDomain::setBin);
  }

  UserCardResponse userCardResponse = this.userCardConverter.toCard(cardDomain, expand);
  try {
    CardExpiry cardExpiry = this.getDecryptedExpiry(cardDomain.getDateExpiry());
    userCardResponse.setExpiry(cardExpiry);
  } catch (NullPointerException | NoSuchPaddingException | NoSuchAlgorithmException |
    InvalidKeyException | IllegalBlockSizeException | BadPaddingException | IllegalArgumentException e) {
    log.warn("UserCardController.getCard: " + e.getMessage(), e);
    throw new UnprocessableEntityException(this.messageError.create(Messages.DECIPHER_ERROR),
      "Decipher error", e);
  }
  return userCardResponse;
}

Refactoring

@Override
public UserCardResponse getCardById(UUID userId, UUID cardId, String expand) {
  UserDomain user = getActiveUser(userId);
  Integer positionCard = validateCardExists(cardId, user);
  CardDomain card = getCardFromUser(user, positionCard);
  defineCardBinData(card);
  UserCardResponse userCardResponse = this.userCardConverter.toCard(card, expand);
  defineCardExpiry(card, userCardResponse);

  return userCardResponse;
}

final User joao = new User("João", "joao@gmail.com");

public class User {
    private final String name;
    private final String email;

    public User(String name, String email) {
        this.name = name;
        this.email = email;
    }    

    ...

}

• immutables/immutables
• rzwitserloot/lombok

Tools