Java Stream collect to map via Collectors with lambda expression

import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

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

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

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

      Map<String,String> map  = 
            langList// w w w. j  av  a2s.c o m
            .stream()
            .collect(Collectors.toMap(Language::getType,
                                      Language::getFirstName,
                                      (oldValue, newValue)  ->  
                                          String.join(", ", oldValue,  newValue))); 
      
      System.out.println(map);
   }
}

class Language {
   private String firstName;
   private double salary;
   private String type;
   
   public Language(String firstName, double salary, String t) {
      this.firstName = firstName;
      this.salary = salary;
      this.type = t; 
       
   }
   public String getType() {
      return this.type;
   }
   public String getFirstName() {
      return firstName;
   }

   public double getSalary() {
      return salary;
   }

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