New concept: Optional #2913

josealonso · 2025-02-10T23:12:13Z

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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… the stub implementation, the reference solution and other required files. Some files must be modified. This is a draft.

josealonso · 2025-02-10T23:25:32Z

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 · 2025-02-11T04:22:02Z

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

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

… are not over yet.

josealonso · 2025-02-11T18:06:21Z

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 · 2025-02-11T18:11:32Z

Which icon should I choose?

kahgoh · 2025-02-12T13:12:07Z

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 · 2025-02-12T14:00:09Z

exercises/concept/tim-from-marketing-2/.meta/src/reference/java/EmployeeService.java

+
+
+class EmployeeService {
+


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?

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

I think this has been resolved.

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.

@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.

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

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. 🤔

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.

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.

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.

exercises/concept/tim-from-marketing-2/src/test/java/EmployeeServiceTest.java

josealonso · 2025-02-14T16:04:33Z

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 :(

…ns have been added. The tests have been corrected and integrated in an IDE. What remains are the hints.md and the icon files, and the gradle files for this exercise.

josealonso · 2025-02-15T01:41:47Z

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

kahgoh · 2025-02-15T13:34:00Z

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 · 2025-02-15T13:37:47Z

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 · 2025-02-17T00:34:06Z

Are the tests passing locally for you?

Yes.

manumafe98 · 2025-02-17T23:55:12Z

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

manumafe98 · 2025-02-17T23:32:41Z

exercises/concept/tim-from-marketing-2/.docs/hints.md

+
+WIP
+
+


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

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

exercises/concept/tim-from-marketing-2/src/test/java/EmployeeServiceTest.java

exercises/concept/tim-from-marketing-2/.meta/design.md

josealonso · 2025-02-19T17:20:19Z

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.

exercises/concept/tim-from-marketing-2/src/test/java/EmployeeServiceTest.java

…ise without streams.

josealonso · 2025-03-06T13:23:31Z

@kahgoh, can you please go through these files and tell me if that's the right approach ? Thanks :)

kahgoh

Hey @josealonso, I have had a look through and I think the exercise is going in the right direction.

In a couple of the comments I mention an about.md. The about.md is shown after they complete the exercise and would be something that will need to eventually be added for the concept.

kahgoh · 2025-02-25T13:53:17Z

exercises/concept/tim-from-marketing-2/build.gradle

+dependencies {
+    testImplementation platform("org.junit:junit-bom:5.10.0")
+    testImplementation "org.junit.jupiter:junit-jupiter"
+    testImplementation "org.assertj:assertj-core:3.25.1"


This suggestion is needed to fix a deprecated warning from Gradle (related to #2905).

Suggested change

testImplementation "org.assertj:assertj-core:3.25.1"

testImplementation "org.assertj:assertj-core:3.25.1"

testRuntimeOnly "org.junit.platform:junit-platform-launcher"

kahgoh · 2025-02-25T23:41:33Z

config.json

+        "name": "tim-from-marketing-2",
+        "uuid": "a6cfc286-8c62-4f5b-8e59-f6bfc4374092",
+        "concepts": [
+          "optional type"


Add hyphen to be consistent with the existing concepts.

Suggested change

"optional type"

"optional-type"

kahgoh · 2025-02-25T23:44:16Z

exercises/concept/tim-from-marketing-2/.docs/introduction.md

+
+## Introduction
+
+The **Optional<T>** type was introduced in Java 8 as a way to indicate that a method will return an object of type T or an empty value. It is present in type signatures of many core Java methods. 


A couple of suggestions for this one:

I think it might be more easier to understand to describe in terms of trying to describe a method that needs to return "no value" instead of "empty" (I'm not sure if everyone would understand what empty means).

I'm not sure I would consider it to be "many" core Java methods (I can only think of the Stream API off the top of my head). I'd suggest removing it or toning it down.

Suggested change

The **Optional<T>** type was introduced in Java 8 as a way to indicate that a method will return an object of type T or an empty value. It is present in type signatures of many core Java methods.

The **Optional<T>** type was introduced in Java 8 as a way to indicate that a method _may_ return a value.

In other words, there is a chance the method returns "no value" at all.

kahgoh · 2025-02-25T23:47:06Z

exercises/concept/tim-from-marketing-2/.docs/introduction.md

+    }
+}
+```
+


I feel like something is missing here, as you've gone straight to how to simplify it. There are probably some basics that we should cover. For example, how do you make an optional? What does empty or present mean?

kahgoh · 2025-02-25T23:50:57Z

exercises/concept/tim-from-marketing-2/.meta/design.md

+The goal of this exercise is to teach the student how to use the Optional API.
+We will use the most common methods: `ifPresent`, `orElse`, `ifPresentOrElse`, `orElseThrow`. 
+The `isPresent` and `get` methods are not presented, since they do not provide any value over an ordinary null check.
+Some methods of the Stream API are needed. This is a bit problematic, since they have not been explained in the current Java track.


I think this sentence is no longer needed.

Suggested change

Some methods of the Stream API are needed. This is a bit problematic, since they have not been explained in the current Java track.

kahgoh · 2025-02-25T23:54:22Z

exercises/concept/tim-from-marketing-2/.meta/src/reference/java/Employee.java

@@ -0,0 +1,53 @@
+import java.util.Objects;
+import java.util.Optional;
+


If we're not expecting students to change this, I think it would be handy to add some comments here. For example:

/** * Holds information about an employee. There is no need to change this file. */

kahgoh · 2025-02-26T00:00:32Z

exercises/concept/tim-from-marketing-2/src/test/java/EmployeeServiceTest.java

+
+    @BeforeEach
+    void setup() {
+        initList();


I found this style of setting up the list (declare the list as field, call initList to populate the list and set up EmployeeService with it here) a little hard to follow because there is quite a bit of jumping around to figure out who the employees are. I'd suggest just setting up the list here:

Suggested change

initList();

listOfEmployees = List.of(

new Employee(1, "Tim", "Marketing"),

new Employee(2, "Joe", "Sales"),

new Employee(3, "Jane", "IT"),

new Employee(4, null, null)

);

kahgoh · 2025-02-26T00:13:27Z

exercises/concept/tim-from-marketing-2/.docs/introduction.md

+## Introduction
+
+The **Optional<T>** type was introduced in Java 8 as a way to indicate that a method will return an object of type T or an empty value. It is present in type signatures of many core Java methods. 
+Before Java 8, developers had to implement null checks:


To keep the introduction focused on Optional and how to use it, I think this may be moved to the about.md.

kahgoh · 2025-03-08T14:45:39Z

exercises/concept/tim-from-marketing-2/src/test/java/EmployeeServiceTest.java

+        listOfEmployees.add(new Employee(1, "Tim", "Marketing"));
+        listOfEmployees.add(new Employee(2, "Joe", "Sales"));
+        listOfEmployees.add(new Employee(3, "Jane", "IT"));
+        listOfEmployees.add(new Employee(4, null, null));


I think there are a number of cases missing, such as a null name and non-null department and non-null name and null department.

kahgoh · 2025-03-08T14:55:06Z

exercises/concept/tim-from-marketing-2/.meta/src/reference/java/EmployeeService.java

I suspect not everyone knows what a "service" class is. I'd suggest using a term that is easier to understand by more people (e.g. EmployeeDatabase?).

Write explanation for the Optional concept, as well as the test file,…

e88392b

… the stub implementation, the reference solution and other required files. Some files must be modified. This is a draft.

josealonso mentioned this pull request Feb 10, 2025

Add concept: optionals #2555

Open

Delete unused file.

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Explain the flatmap operation. The hints.md and introduction.md files…

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… are not over yet.

kahgoh reviewed Feb 12, 2025

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josealonso added 2 commits February 15, 2025 02:11

exercises/concept/tim-from-marketing-2/

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One method definition is now given to the student and more explanatio…

26a1397

…ns have been added. The tests have been corrected and integrated in an IDE. What remains are the hints.md and the icon files, and the gradle files for this exercise.

manumafe98 added the x:size/large label Feb 17, 2025

manumafe98 assigned josealonso Feb 17, 2025

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josealonso added 5 commits February 24, 2025 00:22

Use @beforeeach instead of @BeforeAll.

f94749a

Simplify the solution and the asked methods so streams are not used.

4c5e540

Modify many files, including Hints.md, to adapt them to the new exerc…

4b7a800

…ise without streams.

Delete explanation about flatMap.

9d4cd39

Fix error.

6db542e

Merge branch 'main' into 2555-new-concept-optional

2168b21

josealonso requested a review from manumafe98 February 25, 2025 01:46

kahgoh reviewed Mar 8, 2025

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		## Introduction

		The Optional<T> type was introduced in Java 8 as a way to indicate that a method will return an object of type T or an empty value. It is present in type signatures of many core Java methods.

	The Optional<T> type was introduced in Java 8 as a way to indicate that a method will return an object of type T or an empty value. It is present in type signatures of many core Java methods.
	The Optional<T> type was introduced in Java 8 as a way to indicate that a method _may_ return a value.
	In other words, there is a chance the method returns "no value" at all.

		@@ -0,0 +1,53 @@
		import java.util.Objects;
		import java.util.Optional;

-        initList();
+listOfEmployees =  List.of(
+        new Employee(1, "Tim", "Marketing"),
+        new Employee(2, "Joe", "Sales"),
+        new Employee(3, "Jane", "IT"),
+        new Employee(4, null, null)
+);


		WIP

New concept: Optional #2913

Are you sure you want to change the base?

New concept: Optional #2913

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