Finding the median value from a List of objects using Java 8

Question

I have two classes that are structured like this:

public class Company {
     private List<Person> person;
     ...
     public List<Person> getPerson() {
          return person;
     }
     ...
}

public class Person {
     private Double age;
     ...
     public Double getAge() {
          return age;
     }
     ...
}

Basically the Company class has a List of Person objects, and each Person object can get an Age value.

If I get the List of the Person objects, is there a good way to use Java 8 to find the median Age value among all the Person objects (Stream doesn't support median but is there anything else)?

Double medianAge;
if(!company.getPerson().isEmpty) {
     medianAge = company.getPerson() //How to do this in Java 8?
}

Answer 1

Here's a simplified version of @Holger's answer that also works for IntStream and LongStream, and avoids NoSuchElementException in the case of an empty stream:

int size = someList.size();

//replace 'XXX' with 'Int', 'Long', or 'Double' as desired
return someList.stream().mapToXXX(...).sorted()
    .skip((size-1)/2).limit(2-size%2).average().orElse(Double.NaN);

This will return NaN if the list is empty rather than throwing NoSuchElementException. If you'd prefer to throw a NoSuchElementException instead, simply replace .orElse(Double.NaN) with .getAsDouble().