how to filter list object by using stream map filter in java - list

Question

i want to filter a list of student in java. I have a student class in kotlin like this.
class Student(
var id: String? = null,
var firstName: String? = null,
var lastName: String? = null
) {
constructor(entity: StudentCourse?): this() {
if (entity != null) {
this.id = entity.id.id
this.name = entity.name
}
}
}
class StudentCourse (#EmbeddedId open var id: StudentCourseId) {
constructor() : this(StudentCourseId())
open var name: Boolean? = null
}
#Embeddable
open class StudentCourseId: Serializable {
open var id: String? = null
open var deptName: String? = null
}
this is the list i want to filter :
var students: List<Student> = listOf(
Student("14adbv45", "dan", "GEG"),
Student("96adbv42","Bob", "Bowyer"),
Student("30adbv45","Emily", "Eden")
)
I do this
List<students> studentListContainsFirstNameBob = students.stream()
.map(StudentCourse)
.filter(e -> e.getFirstName.equals("Bob"))
.flatMap(List::stream);
but it doesn't work.
How can i do it please

Answer 1

There are multiple issues in your code.
For example in this part:
constructor(entity: StudentCourse?): this() {
if (entity != null) {
this.id = entity.id.id
this.name = entity.name
}
}
The entity.name refers to StudentCourse#name, but this property is actually of Boolean type, so comparing it to String doe snot make much sense. You have also doubled .id which is incorrect.
Next thing, I am not sure what this snipped should do, was the intention to link a student with given course? If so, you would probably like to add a list of students to a course, or a list of courses to a student (which sounds more correct).
Finally, when it comes to filtering a list, you can get students with first name Bob in this way:
var studentListContainsFirstNameBob: List<Student> = students
.filter { it.firstName.equals("Bob") }
.toList()
Mind the it variable refers to the element from the list, it could also be written:
var studentListContainsFirstNameBob: List<Student> = students
.filter { student -> student.firstName.equals("Bob") }
.toList()