New concept: Optional

[josealonso]

Write explanation for the Optional concept, as well as the test file, the stub implementation, the reference solution and other required files. Some files must be modified. This is a draft.

This solves #2555

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Reviewer Resources:

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[josealonso]

I just committed a first draft. Don't worry about the linting errors, I will sort them out during this week.
I'd like to receive feedback about the reference solution and the test file, the bulk of the work is done.

• Is there an exercise for the generics concept ? That is a prerequisite for this concept.
• If that concept is not explained on the Java track, I can adapt it from other track.

@kahgoh @jagdish-15

[kahgoh]

Thanks @josealonso! I plan to have a look at the draft soon.

In regards to the generics concept, it is covered as generics type.

[josealonso]

Thanks @josealonso! I plan to have a look at the draft soon.

In regards to the generics concept, it is covered as generics type.

Thanks for the link to the generic-types exercise!! Shame on me

[josealonso]

Which icon should I choose?

[kahgoh]

Did you mean the icon for the exercise? They get added to exercism/icons repository, though that can be done after the exercise is added. We'll have to make one, but I think it will be the same icon as the original Tim From Marketing, but with a "2" in the top right corner. Compare Wizards and Warriors and Wizards and Warriors 2 for an example.

[kahgoh]

To be honest, I didn't quite get the purpose of these two methods (getAllTheEmployeesById and getEmployeeById) especially as we're not expecting the students to implement these and I don't think its clear when we expect them to call them.

Since the Employee have methods that return Optional objects, I'd suggest having the test pass Employee objects or a List of them instead.

Is it also worth having a task for where the student has to return an Optional as well?

[josealonso]

Thanks for your feedback.
I agree, I did it like that because I had all the code in one single file.

[josealonso]

I think this has been resolved.

[kahgoh]

I had another thought - the getEmployeeById could also be left up to the student to implement. We already have the foreach concept, so they could use that to find the employee and that'll give them the chance to practice making an Optional object (assuming they are looking through a List<Employee>) and there would be no need for streams in the class.

[josealonso]

@kahgoh, despite I spent many hours creating this exercise, I have to admit it's probably a bit complex for a learning exercise. This is what I propose:

• Leaving this one for a future practice exercise.
• Create a concept exercise for Streams first. And maybe another one for Suppliers or functional interfaces, based on my article or a similar one.

[josealonso]

I'll leave a longer answer tomorrow, but I just wanted to thank you for your support and clarify that my struggle is due to being my first exercise designed from scratch and also because I wasn't not very familiar with the Optional API.
I would cover more simple streams operations in a first Streams learning exercise, like map, filter and other simple operations.
@kahgoh

[josealonso]

I had another thought - the getEmployeeById could also be left up to the student to implement. We already have the foreach concept, so they could use that to find the employee and that'll give them the chance to practice making an Optional object (assuming they are looking through a List<Employee>) and there would be no need for streams in the class.

Are you saying I can implement the same methods without using streams ? I'm not sure that's doable. 🤔

[kahgoh]

I was thinking the EmployService could take in a List<Employee> in the constructor, so then the students could be tasked with finding the Employee by id. I imagine the stub would like this:

class EmployeeService {
  public EmployeeService(List<Employee> employees) {
    throw new UnsupportedOperationException("Please implement the EmployeeService constructor");
  }

  public Optional<Employee> getEmployeeById(int id) {
     throw new UnsupportedOperationException("Please implement the EmployeeService.getEmployeeById() method");
  }
}

Students can still make a solution for this using a for / while loop that goes through the list until it finds the Employee. Here's one rough way:

for (Employee candidate: employeesList) {
  if (Objects.equals(candidate.getId(), Optional.of(id)) {
    return Optional.of(candidate);
  }
}

return Optional.empty();

Alternatively, I think passing the method a List<Employee> to the method would also work.

[josealonso]

I was thinking the EmployService could take in a List<Employee> in the constructor, so then the students could be tasked with finding the Employee by id. I imagine the stub would like this:

class EmployeeService {
  public EmployeeService(List<Employee> employees) {
    throw new UnsupportedOperationException("Please implement the EmployeeService constructor");
  }

  public Optional<Employee> getEmployeeById(int id) {
     throw new UnsupportedOperationException("Please implement the EmployeeService.getEmployeeById() method");
  }
}

Students can still make a solution for this using a for / while loop that goes through the list until it finds the Employee. Here's one rough way:

for (Employee candidate: employeesList) {
  if (Objects.equals(candidate.getId(), Optional.of(id)) {
    return Optional.of(candidate);
  }
}

return Optional.empty();

Alternatively, I think passing the method a List<Employee> to the method would also work.

Thanks @kahgoh. I'll try to change it this weekend. I was stuck, because I designed this exercise to try to mimic the access to a database. But you're right, I made it too complex.

[josealonso]

Thanks for your help, @kahgoh. Take a look when you have a chance. I think I did it the way you suggested. I'm sure it can be improved, but streams are not used in the reference solution.

[josealonso]

Did you mean the icon for the exercise? They get added to exercism/icons repository, though that can be done after the exercise is added. We'll have to make one, but I think it will be the same icon as the original Tim From Marketing, but with a "2" in the top right corner. Compare Wizards and Warriors and Wizards and Warriors 2 for an example.

Who can make that icon? I'm sorry I don't know how to edit a simple icon :(

[josealonso]

I don't understand why the java-test-runner failed, @kahgoh. It probably has to do with some missing configuration files,

[kahgoh]

Who can make that icon? I'm sorry I don't know how to edit a simple icon :(

That's fine, we can do that later. For now, let's just work on the concept content.

[kahgoh]

I don't understand why the java-test-runner failed, @kahgoh. It probably has to do with some missing configuration files,

Its a bit hard to find, but this appears in the log:

tim-from-marketing-2: exemplar solution did not pass the tests

Are the tests passing locally for you?

[josealonso]

Are the tests passing locally for you?

Yes.

[manumafe98]

Maybe this doc on configlet could be useful for you as well to check

[manumafe98]

@josealonso I suggest you to use this vscode extension for markdown linting, you will be able to solve them easily

[josealonso]

Thanks for the suggestion!! I use Intellij, there might be a similar plugin for this IDE, I guess.

[josealonso]

Maybe this doc on configlet could be useful for you as well to check

Thanks, I went through it already. I'll have to read it again.