implementing Custom Filtering in Java Streams When Using Optional Values from a List
I've hit a wall trying to I'm sure I'm missing something obvious here, but I tried several approaches but none seem to work. I'm currently working with a scenario with filtering a list of objects in Java using streams, particularly when some of the objects have optional values that may or may not be present. I'm using Java 11 and trying to filter a list of `Person` objects based on an optional `age` attribute. The goal is to retrieve all `Person` instances where the `age` is present and greater than a certain threshold. Here’s the structure of the `Person` class: ```java public class Person { private String name; private Optional<Integer> age; public Person(String name, Optional<Integer> age) { this.name = name; this.age = age; } public Optional<Integer> getAge() { return age; } @Override public String toString() { return name + " (age: " + age.orElse(null) + ")"; } } ``` I have a list of `Person` objects as follows: ```java List<Person> people = Arrays.asList( new Person("Alice", Optional.of(30)), new Person("Bob", Optional.empty()), new Person("Charlie", Optional.of(25)), new Person("David", Optional.of(40)) ); ``` I attempted to use the following stream pipeline to filter the list: ```java List<Person> filtered = people.stream() .filter(p -> p.getAge().isPresent() && p.getAge().get() > 26) .collect(Collectors.toList()); ``` However, I noticed that the filtered list doesn't include `Alice` and `David`, which is what I expected. Instead, it seems to return an empty list. I also tried using `map` to extract the age first, but that led to a `NoSuchElementException` if I tried to get an age that wasn't present. Based on the filtering logic, I assumed that `isPresent()` would work correctly in combination with the filter, but I must be missing something. Could someone guide to understand why my filtering logic isn't working as expected? Is there a better approach to handle the optional filtering in this case? Any guidance would be greatly appreciated! My development environment is Ubuntu. For context: I'm using Java on Linux. For reference, this is a production desktop app. I appreciate any insights!