Update a existing function using stream api

Question

I have the below method that I would like to rewrite using streams.

I was thinking to write a method and call that using stream().forEach() but not sure on how to map the return.

List<Student> students  = new ArrayList<>();
        if(myService.getData()!=null){
           for(Person person: myService.getData().getPersons()) {
               Student student = new Student();
               student.setGender(person.getSex());
               student.setGpa(person.getScore);
               students.add(student);
           }
        }

Honestly, using Streams will not improve this code. I would leave it as it is. — VGR
– VGR, Commented Jan 18, 2021 at 19:41
@VGR I completely agree. Just that I want to make the code look cleaner. :) — Jeeppp
– Jeeppp, Commented Jan 18, 2021 at 19:48
I’m pretty sure it will look cleaner as you have it, than any Stream-based solution could look. — VGR
– VGR, Commented Jan 18, 2021 at 19:53

Ryuzaki L · Accepted Answer · 2021-01-19 11:58:15Z

1

You can use Optional and then use the constructor to create Student object

public Student(String sex, Integer score)  {
  this.sex = sex;
  this.score = score;
}

And then stream the Person list to create Student

List<Student> students = Optional.ofNullable(myService.getData())
        .map(data->data.getPersons().stream().map(per->new Student(per.getSex(),per.getScore())).collect(Collectors.toList())
        .orElse(Collections.emptyList();

You can also add null check for getPersons()

List<Student> students = Optional.ofNullable(myService.getData())
        .filter(data->data.getPersons()!=null)
        .map(data->data.getPersons().stream().map(per->new Student(per.getSex(),per.getScore())).collect(Collectors.toList())
        .orElse(Collections.emptyList();

edited Jan 19, 2021 at 11:58

answered Jan 18, 2021 at 19:17

Ryuzaki L

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2 Comments

Naman Over a year ago

You don't really need an Optional here. The stream section could just replace the block within the if.

Holger Over a year ago

Since the stream operation doesn’t specify to return an ArrayList, there is no point in using ArrayList in the fallback case. Just use Collections.emptyList() instead.

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