我是一個相當新的 Java 程序員，我目前正在學習流。我正在嘗試使用流來獲取每個部門的工資并對其進行平均。我已經能夠添加工資或平均工資，但我無法弄清楚我將如何按部門執行此操作。這是我到目前為止的代碼。 import java.util.Arrays; import java.util.Comparator; import java.util.List; import java.util.Map; import java.util.function.Function; import java.util.stream.Collectors;public class AverageSalariesDept {public static void main(String[] args) {  Employee[] employees = {     new Employee("Jason", "Red", 5000, "IT"),     new Employee("Ashley", "Green", 7600, "IT"),     new Employee("Matthew", "Indigo", 3587.5, "Sales"),     new Employee("James", "Indigo", 4700.77, "Marketing"),     new Employee("Luke", "Indigo", 6200, "IT"),     new Employee("Jason", "Blue", 3200, "Sales"),     new Employee("Wendy", "Brown", 4236.4, "Marketing")};  List<Employee> list = Arrays.asList(employees);  Function<Employee, String> byDepartment = Employee::getDepartment;  Function<Employee, Double> bySalary = Employee::getSalary;  Comparator<Employee> compSalaries =   Comparator.comparing(byDepartment).thenComparing(bySalary);  list.stream()           .sorted(compSalaries)             .forEach(System.out::println);   System.out.printf("Average of Employees' salaries: %.2f%n",     list.stream()         .mapToDouble(Employee::getSalary)         .average()         .getAsDouble()); } }