Optional vs. null. What is the purpose of Optional in Java 8? [duplicate]

Question

In Java 8 you can return an Optional instead of a null. Java 8 documentation says that an Optional is "A container object which may or may not contain a non-null value. If a value is present, isPresent() will return true and get() will return the value."

In practice, why is this useful? Also, is there any case where using null would be preferred? What about performance?

Answer 1

In practice, why is this useful?

For example let's say you have this stream of integers and you're doing a filtering:

int x = IntStream.of(1, -3, 5)                  .filter(x -> x % 2 == 0)                  .findFirst(); //hypothetical assuming that there's no Optional in the API 

You don't know in advance that the filter operation will remove all the values in the Stream.

Assume that there would be no Optional in the API. In this case, what should findFirst return?

The only possible way would be to throw an exception such as NoSuchElementException, which is IMO rather annoying, as I don't think it should stop the execution of your program (or you'd have to catch the exception, not very convenient either) and the filtering criteria could be more complex than that.

With the use of Optional, it's up to the caller to check whether the Optional is empty or not (i.e if your computation resulted in a value or not).

With reference type, you could also return null (but null could be a possible value in the case you filter only null values; so we're back to the exception case).

Concerning non-stream usages, in addition to prevent NPE, I think it also helps to design a more explicit API saying that the value may be present or not. For example consider this class:

class Car {    RadioCar radioCar; //may be null or not     public Optional<RadioCar> getRadioCar() {         return Optional.ofNullable(radioCar);    } } 

Here you are clearly saying to the caller that the radio in the car is optional, it might be or not there.