Monday, May 25, 2015

Java 8: Filtering an Optional

In my previous post, I wrote about how you can use optionals to model the absence of a value. Optionals also contain a useful filter method, which takes a predicate as an argument. If a value is present in the Optional object and the predicate is satisfied, the filter method returns that value; otherwise it returns an empty Optional object.

For example, let's suppose that the Phone class of the Person/Phone/Camera/Resolution model has a method to get the operating system of the phone, and we want to get the camera resolution of "Android" phones only. We can modify the getPhoneCameraResolution method to use a filter, as shown below:

public Resolution getPhoneCameraResolution(final Optional<Person> person) {
    person.flatMap(Person::getPhone)  // returns Optional<Phone>
          .filter(phone -> phone.getOS() == OS.Android) // match Android phones only
          .flatMap(Phone::getCamera) // returns Optional<Camera>
          .map(Camera::getResolution) // returns Optional<Resolution>
          .orElse(Resolution.UNKNOWN); // returns Resolution or UNKNOWN if not found

Related posts:
Java 8: Using Optional Objects

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