Stream Collector

     // Accumulate names into a List

     List<String> list = people.stream().map(Person::getName).collect(Collectors.toList());



     // Accumulate names into a TreeSet

     Set<String> set = people.stream().map(Person::getName).collect(Collectors.toCollection(TreeSet::new));



     // Convert elements to strings and concatenate them, separated by commas

     String joined = things.stream()

                           .map(Object::toString)

                           .collect(Collectors.joining(", "));



     // Compute sum of salaries of employee

     int total = employees.stream()

                          .collect(Collectors.summingInt(Employee::getSalary)));



     // Group employees by department

     Map<Department, List<Employee>> byDept

         = employees.stream()

                    .collect(Collectors.groupingBy(Employee::getDepartment));



     // Compute sum of salaries by department

     Map<Department, Integer> totalByDept

         = employees.stream()

                    .collect(Collectors.groupingBy(Employee::getDepartment,

                                                   Collectors.summingInt(Employee::getSalary)));



     // Partition students into passing and failing

     Map<Boolean, List<Student>> passingFailing =

         students.stream()

                 .collect(Collectors.partitioningBy(s -> s.getGrade() >= PASS_THRESHOLD));