Java 比较两个列表并分配到新的对象列表

我有一个包含班级员工对象的列表，其他列表包含班级部门对象，如下所示：-

Class Employee {
String emolpyee_id;
String employee_Name;
}
Class Dapartment {
String emolpyee_id;
String employee_Department;
}

List<Employee> empl =  = new ArrayList<>();
List<Dapartment> depart =  = new ArrayList<>();

Employee e1 = new Employee("12","Testing");
Employee e2 = new Employee("16","TestingOthers");

Dapartment d1 = new Dapartment("12","IT");
Dapartment d2 = new Dapartment("12","Networking");
Dapartment d3 = new Dapartment("12","Financing");
Dapartment d4 = new Dapartment("16","IT");
Dapartment d5 = new Dapartment("16","Networking");

empl.add(e1);
empl.add(e2);

depart.add(d1);
depart.add(d2);
depart.add(d3);
depart.add(d4);
depart.add(d5);

Class ExpectedResult {
String emolpyee_id;
String employee_Name;
List<String> employee_Department;
}

List<ExpectedResult> expResult = {{"12","Testing",{"IT","Networking","Financing"}} ,{"16","TestingOthers",{"IT","Networking"}}}

我知道我们可以使用普通for循环执行此操作，但我想使用lambda和java 8流实现此输出。

首先使用groupingBy将列表流到映射中，这是作为键的员工id映射，值是部门列表

Map<String, List<String>> groupby = depart.stream().
            collect(Collectors.groupingBy(Department::getEmolpyee_id, Collectors.mapping(Department::getEmployee_Department, Collectors.toList())));

注意，对于列出员工\部门，您可能会得到null；如果groupby映射不包含员工id和值，则在ExpectedResult中

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旁注：类是小写的，类是错误的，部门拼写更正

Stackoverflow不是让你编程的地方。如果您是Java 8新手，为什么不读一本教程或一本书呢？谢谢您的回复..这真的节省了我的时间..再次非常感谢。。。

List<ExpectedResult> expected = empl.stream().
            map(emp-> new ExpectedResult(emp.getEmolpyee_id(),emp.getEmployee_Name(),groupby.get(emp.getEmolpyee_id()))).collect(Collectors.toList());