16. Optional Type

Optional Type

In this section, you will learn to:

• Use the java.util.Optional class
• Use Optional with the Stream API

What is an Optional Type?

• java.util.Optional is a container object that may or may not contain a single, non-null value.
• Optional is an alternative to using null to represent the absence of a value.

Optional Type Example

Optional Types are often returned by terminal operations on streams.

int getTopScore(List<Student> students) {
 return students.stream()
     .filter(Objects::nonNull)
     .mapToInt(Student::getScore)
     .max()
     .orElse(0);
}

Here, the max() method actually returns an OptionalInt, not an int. If the students list is empty, the max() method will return an empty optional.

If max() returns an OptionalInt with a value, that value will be used. However, if max() returns OptionalInt.empty(), the call to orElse() makes sure that a default value of 0 will be returned.

This example also shows you how, in addition to Optional<T>, Java also has optional types that are specialized for int, long, and double primitives. These classes avoid the need for auto-boxing and auto-unboxing of their values.

When to Use Optional Types

When you're designing Java APIs, you should consider using Optional instead of null to represent the absence of values.

Optional can have methods invoked on it without throwing NullPointerException. The Stream API uses optional types for many of its terminal operations.

However, optionals can sometimes lead to more verbose code by forcing you to call .get() whenever you want the value.