Optional Values
Instead of passing using null references optional values can be wrapped in
a Optional instances. This type is typically used in APIs
to express the possibility that a method may not return a value, for example
Stream.max() may not have a
return value on an empty stream.
The Optional type is designed to be used in a functional way: It owns the
control flows, we simply declare what to do if a value is present or missing.
If you find yourself writing code like if (optional.isPresent()) { ... } or
you are calling Optional.get() you’re most likely on the
wrong track.
Since Java 8
import java.util.Optional;
public class OptionalValues {
static void work(Optional<String> task) {
// Obtain a fixed default
var myTask1 = task.orElse("Clean the kitchen.");
System.out.println(myTask1);
// Calculate the default value if required
var myTask2 = task.orElseGet(OptionalValues::createTask);
System.out.println(myTask2);
// Perform an operation if a value exist:
task.ifPresent(System.out::println);
// Perform an operation if a value exist or do something else:
task.ifPresentOrElse(System.out::println, OptionalValues::idle);
// The optional value can be mapped (if it exists):
task.map(String::toUpperCase).ifPresent(System.out::println);
// The optional value can be filtered (if it exists):
task.filter(t -> t.contains("coding")).ifPresent(System.out::println);
}
static String createTask() {
return "Find random Task.";
}
static void idle() {
System.out.println("Just lazy today.");
}
public static void main(String[] args) {
System.out.println("Our task today:");
work(Optional.of("Do some coding."));
System.out.println("No Task today:");
work(Optional.empty());
}
}
This snippet at GitHub