Java Stream collect to Collection for custom object attribute

import java.util.Arrays;
import java.util.List;
import java.util.SortedSet;
import java.util.TreeSet;
import java.util.stream.Collectors;

public class Main {
   public static void main(String[] args) {
      Language[] langArray = { //
            new Language("CSS",  55555), //
            new Language("HTML", 66666), //
            new Language("Java", 44444.5), //
            new Language("Javascript", 77777.77), //
            new Language("C++", 88888), //
            new Language("C",   33333), //
            new Language("SQL", 99999.4) };//

      List<Language> langList = Arrays.asList(langArray);

      langList.stream().forEach(System.out::println);

      SortedSet<String> uniqueSortedNames = 
             langList/*from  w w  w .  jav  a2s. c o m*/
             .stream()
             .map(Language::getFirstName)
             .collect(Collectors.toCollection(TreeSet::new));

      System.out.println(uniqueSortedNames);
   }
}

class Language {
   private String firstName;
   private double salary;

   public Language(String firstName, double salary) {
      this.firstName = firstName;
      this.salary = salary;
   }

   public String getFirstName() {
      return firstName;
   }

   public double getSalary() {
      return salary;
   }

   @Override
   public String toString() {
      return String.format("%-20s %8.2f", getFirstName(), getSalary());
   }
}