Stream Stream 객체 groupingBy

[주인장]

[문제]

Employee 리스트를 부서(Department)별로 그룹화하세요.

[데이터]

new Employee("A001", "Kim", "IT")

new Employee("A002", "Lee", "HR")

new Employee("A003", "Park", "IT")

new Employee("A004", "Choi", "Sales")

new Employee("A005", "Jung", "HR")

[요구사항]

- `groupingBy()`로 부서별 그룹화

- 각 부서별 직원 출력

[소스]

import java.util.Arrays;

import java.util.List;

import java.util.Map;

import java.util.stream.Collectors;

public class StreamObjectGrouping {

    // 간단한 Employee 클래스

    static class Employee {

        String id;

        String name;

        String department;

        public Employee(String id, String name, String department) {

            this.id = id;

            this.name = name;

            this.department = department;

        }

        public String getDepartment() {

            return department;

        }

        @Override

        public String toString() {

            return id + " - " + name;

        }

    }

    public static void main(String[] args) {

        List<Employee> employees = Arrays.asList(

            new Employee("A001", "Kim", "IT"),

            new Employee("A002", "Lee", "HR"),

            new Employee("A003", "Park", "IT"),

            new Employee("A004", "Choi", "Sales"),

            new Employee("A005", "Jung", "HR")

        );

        System.out.println("원본 직원 리스트:");

        employees.forEach(System.out::println);

        // groupingBy()로 부서별 그룹화

        Map<String, List<Employee>> byDepartment = employees.stream()

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

        System.out.println("\n부서별 직원:");

        byDepartment.forEach((dept, emps) -> {

            System.out.println("[" + dept + "]");

            emps.forEach(e -> System.out.println("  " + e));

        });

    }

}