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What are Optional types? ​

Basically, every method that might return a null value will return an Optional in AT4J. This is a way to avoid NullPointerExceptions in your code. This type was introduced in Java 8 and is a container object that may or may not contain a non-null value. If a value is present, isPresent() will return true, and get() will return the value.

Old code:

java
  TranslationResponse translation = azureApi.translate(text).join();
  if (translation != null) {
    translation.getFirstResult().getTranslations().forEach(ExampleApi::log);
  }

New code:

java
  azureApi.translate(text).ifPresent(response ->
  response.getFirstResult().getTranslations().forEach(ExampleApi::log));

You can imagine an Optional like a box that may or may not contain a value. Before accessing this value, you have to unpack this box first.

Methods ​

get() ​

CAUTION

You should avoid using the get method as it can throw a NoSuchElementException if the value is not present. It is recommended to use the isPresent method to check if the value is present before calling the get method. If you are sure that the value is present, you can use the orElse method to provide a default value if the value is not present.

The get method returns the value if present, otherwise throws a NoSuchElementException.

java
TranslationResponse translation = azureApi.translate(text).get();
translation.getFirstResult().getTranslations().forEach(ExampleApi::log);

isPresent() ​

The isPresent method returns true if the Optional contains a non-null value, otherwise false.

java
Optional<TranslationResponse> translation = azureApi.translate(text);
if (translation.isPresent()) {
  translation.get().getFirstResult().getTranslations().forEach(ExampleApi::log);
}

ifPresent(Consumer<? super T> consumer) ​

The ifPresent method takes a Consumer as an argument and executes the consumer if the Optional contains a non-null value.

java
azureApi.translate(text).ifPresent(response ->
  response.getFirstResult().getTranslations().forEach(ExampleApi::log));

orElse(T other) ​

The orElse method returns the value if present, otherwise returns the specified value.

java
TranslationResponse translation = azureApi.translate(text).orElse(new TranslationResponse());
translation.getFirstResult().getTranslations().forEach(ExampleApi::log);

orElseGet(Supplier<? extends T> other) ​

The orElseGet method returns the value if present, otherwise returns the result of the specified Supplier.

java
TranslationResponse translation = azureApi.translate(text).orElseGet(() -> new TranslationResponse());
translation.getFirstResult().getTranslations().forEach(ExampleApi::log);

orElseThrow() ​

The orElseThrow method returns the value if present, otherwise throws an exception.

java
TranslationResponse translation = azureApi.translate(text).orElseThrow();
translation.getFirstResult().getTranslations().forEach(ExampleApi::log);

map(Function<? super T, ? extends U> mapper) ​

The map method applies the given function to the value if present, otherwise returns an empty Optional.

java
Optional<String> translation = azureApi.translate(text).map(response -> response.getFirstResult().getTranslations().getFirst().getText());
translation.ifPresent(System.out::println);

filter(Predicate<? super T> predicate) ​

The filter method returns an Optional containing the value if present and the value matches the given predicate,

java
Optional<Translation> translation = azureApi.translate(text).flatMap(response -> response.getFirstResult().getTranslations().stream().findFirst());
translation.filter(t -> t.getLanguageCode().equals("en")).ifPresent(ExampleApi::log);

flatMap(Function<? super T, Optional<U>> mapper) ​

The flatMap method applies the given function to the value if present, otherwise returns an empty Optional.

java
Optional<Translation> translation = azureApi.translate(text).flatMap(response -> response.getFirstResult().getTranslations().stream().findFirst());
translation.ifPresent(ExampleApi::log);

Further Reading ​