Populating List of Objects using constructor with parameters

Question

I need to populate list of class Student:

class Student {
    String firstName;
    String lastName;
    public Student(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }

Here is the generator method signature:

public List<Student> generateRandomStudents(int quantity) {
List<Student> students;
// List is populated by required quantity of students
return students;

What I have tried:

List<Student> students = Stream
    .of(new Student(getRandomStringFromFile("firstnames.txt"), getRandomStringFromFile("lastnames.txt")))
    .limit(quantity)
    .collect(Collectors.toList());

creates only 1 student. 2) Tried using Stream.generate, but it works only with Supplier and I can't use my arguments for the constructor.

Can you show how you have tried Stream.generate? You do need a supplier here. — Sweeper
– Sweeper, Commented Apr 15, 2021 at 11:27
..or think of using IntStream.range as if you would loop, mapping to a new Student object each time. — Naman
– Naman, Commented Apr 15, 2021 at 11:29

Peter Walser · Accepted Answer · 2021-04-15 11:35:43Z

3

Stream.of(new Student(..)) generates a stream of just that single element.

What you instead want is to have a Supplier<Student> which can produce a random Student, and then use Stream.generate(Supplier<?>) to generate an endless stream of random students (which you later limit):

Supplier<Student> randomStudent = () -> new Student(
        getRandomStringFromFile("firstnames.txt"), 
        getRandomStringFromFile("lastnames.txt"));

List<Student> students = Stream.generate(randomStudent)
        .limit(quantity)
        .collect(Collectors.toList());

or inlined:

List<Student> students = Stream
        .generate(() -> new Student(
                getRandomStringFromFile("firstnames.txt"),
                getRandomStringFromFile("lastnames.txt")))
        .limit(quantity)
        .collect(Collectors.toList());

answered Apr 15, 2021 at 11:35

Peter Walser

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