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

Reviewer Resources:

Track Policies

… 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

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

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.

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

config.json

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

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

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

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)

);

I couldn't do it like that, because I was mutating a list element in the null case. I will revisit it.

I'm not quite sure where you are mutating the list element, but if a test needs different data, I'd suggest setting up the test data in the test methods instead.

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

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

josealonso · 2025-03-14T02:02:48Z

I will continue tomorrow.

kahgoh · 2025-03-14T06:58:28Z

I will continue tomorrow.

No worries @josealonso . There's no hurry for this one, so feel free to take longer if you need to

josealonso · 2025-03-14T18:55:48Z

I will continue tomorrow.

No worries @josealonso . There's no hurry for this one, so feel free to take longer if you need to

The value of concepts.uuid is a zero-length string.
I thought it had to match the exercises.uuid, but doing that produced an error, so I left it empty.
It's the only error in the configlet phase.
The tests are failing to build even locally, it might be a configuration issue.

I addressed all the suggestions you made, except using List.of() instead of a function in the tests.

Please tell me how to fix the two errors mentioned above and fell free to suggest any improvements.

Thanks @kahgoh!

kahgoh · 2025-03-19T09:44:46Z

The value of concepts.uuid is a zero-length string.
I thought it had to match the exercises.uuid, but doing that produced an error, so I left it empty.

They are two different UUIDs. You can generate one using configlet uuid.

The tests are failing to build even locally, it might be a configuration issue.

I'm a little confused as to which solution to look at as there is one in src/reference/java and I can also see an implementation in src/main/java. I assume the one in src/main/java is just a work in progress (ultimately, we want to end up with the working one in src/referece/java). Could you let me know how you are currently testing?

Btw, to test against the reference solution, you can go into the exercises directory and run ./gradlew :concept:tim-from-marketing-2:test.

kahgoh · 2025-03-19T12:51:38Z

I've just tried running the tests locally. The failing tests have the following messages:

EmployeeDatabaseTest > Retrieve employee details by id when department is null and name is not null FAILED
    org.opentest4j.AssertionFailedError:
    expected: "No employee found for id: 6"
     but was: "6 - Alice - null"
        at [email protected]/jdk.internal.reflect.DirectConstructorHandleAccessor.newInstance(DirectConstructorHandleAccessor.java:62)
        at [email protected]/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:502)
        at app//EmployeeDatabaseTest.retrieveEmployeeDetailsById_whenDepartmentIsNull(EmployeeDatabaseTest.java:92)

and

EmployeeDatabaseTest > Retrieve employee details by id when the id does not exist FAILED
    org.opentest4j.AssertionFailedError:
    expected: "No employee found for id: 10"
     but was: "That id does not exist: 10"
        at [email protected]/jdk.internal.reflect.DirectConstructorHandleAccessor.newInstance(DirectConstructorHandleAccessor.java:62)
        at [email protected]/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:502)
        at app//EmployeeDatabaseTest.retrieveEmployeeDetailsById_forANonExistingId(EmployeeDatabaseTest.java:100)

I ran them against the .meta/src/reference using gradlew :concept:tim-from-marketing-2:test. Can you see why these test may fail?

josealonso · 2025-03-19T13:09:25Z

The value of concepts.uuid is a zero-length string.
I thought it had to match the exercises.uuid, but doing that produced an error, so I left it empty.

They are two different UUIDs. You can generate one using configlet uuid.

The tests are failing to build even locally, it might be a configuration issue.

I'm a little confused as to which solution to look at as there is one in src/reference/java and I can also see an implementation in src/main/java. I assume the one in src/main/java is just a work in progress (ultimately, we want to end up with the working one in src/referece/java). Could you let me know how you are currently testing?
Oh, sorry, I thought both files had the same content. I changed only the file name, as you suggested. I might have changed something else without realizing it. Let me take a look tonight (in Europe).
Thanks for the hint, because I couldn't run the tests locally.

Btw, to test against the reference solution, you can go into the exercises directory and run ./gradlew :concept:tim-from-marketing-2:test.
Thanks, hopefully this command will work locally!

josealonso · 2025-03-19T13:11:31Z

I've just tried running the tests locally. The failing tests have the following messages:

EmployeeDatabaseTest > Retrieve employee details by id when department is null and name is not null FAILED
    org.opentest4j.AssertionFailedError:
    expected: "No employee found for id: 6"
     but was: "6 - Alice - null"
        at [email protected]/jdk.internal.reflect.DirectConstructorHandleAccessor.newInstance(DirectConstructorHandleAccessor.java:62)
        at [email protected]/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:502)
        at app//EmployeeDatabaseTest.retrieveEmployeeDetailsById_whenDepartmentIsNull(EmployeeDatabaseTest.java:92)

and

EmployeeDatabaseTest > Retrieve employee details by id when the id does not exist FAILED
    org.opentest4j.AssertionFailedError:
    expected: "No employee found for id: 10"
     but was: "That id does not exist: 10"
        at [email protected]/jdk.internal.reflect.DirectConstructorHandleAccessor.newInstance(DirectConstructorHandleAccessor.java:62)
        at [email protected]/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:502)
        at app//EmployeeDatabaseTest.retrieveEmployeeDetailsById_forANonExistingId(EmployeeDatabaseTest.java:100)

I ran them against the .meta/src/reference using gradlew :concept:tim-from-marketing-2:test. Can you see why these test may fail?

I'll let you know if I can run the tests locally. Thanks!

kahgoh · 2025-03-19T09:54:31Z

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

+
+```java
+Employee nullableEmployee = new Employee();
+Optional<Employee> nullableEmployee = Optional.ofNullable(employee);


nullableEmployee is never null here. I think a better example would be to call a method that might return null.

I'd also suggest Optional.empty.

kahgoh · 2025-03-19T12:16:57Z

concepts/optional-type/introduction.md

+If the employee _may_ be not present, the static [ofNullable][optional-ofNullable-javadoc] method must be used:
+
+```java
+Employee nullableEmployee = new Employee();


I think a better example would be calling a method that might return null (in this example, it is never null). I'd also suggest calling the variable optionalEmployee because nullable tends mean you can assign a null value to it.

kahgoh · 2025-03-19T12:28:37Z

concepts/optional-type/introduction.md

+
+## Basic methods
+
+If a value is present, the [isPresent][optional-isPresent-javadoc] method returns true and the [get][optional-get-javadoc] method returns the value.


We've switch from "may return a value" or "no value" from the introduction to "present" here. I think it would help to define what "present" and "empty" mean either here or back in the introduction.

kahgoh · 2025-03-19T13:12:57Z

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

+    }
+
+    @Test
+    @Tag("task:3")


There are only two tasks in the instructions, so the tags should be only "task:1" or "task:2". They should line up with the corresponding task in the instructions.

kahgoh · 2025-03-19T13:25:59Z

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

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


I'm not quite sure where you are mutating the list element, but if a test needs different data, I'd suggest setting up the test data in the test methods instead.

kahgoh · 2025-03-19T13:33:55Z

concepts/optional-type/links.json

@@ -0,0 +1,2 @@
+[]


Suggest a link to the Javadocs for Optional. See the links.json for the Lists concept for an example.

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.

fbe3f46

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

0abf443

… 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/

5c143e1

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 Large amount of work label Feb 17, 2025

manumafe98 assigned josealonso Feb 17, 2025

manumafe98 requested changes 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

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

kahgoh reviewed Mar 8, 2025

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Make some improvements, although it's not complete yet.

53cbbda

josealonso force-pushed the 2555-new-concept-optional branch from 2168b21 to 53cbbda Compare March 14, 2025 01:44

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

145d49b

josealonso added 7 commits March 14, 2025 17:21

Make more improvements, including a new "about.md" document.

9b20d73

Add two tests.

c227af5

Fix configuration issues.

8f2afa8

Changed some prerequisites names.

27b6662

The if-staments concept is now called if-else-statements.

f047509

Add optional-type to the concepts array.

ec171ee

Fix configlet issues.

41076df

kahgoh reviewed Mar 19, 2025

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


		## Basic methods

		If a value is present, the [isPresent][optional-isPresent-javadoc] method returns true and the [get][optional-get-javadoc] method returns the value.

New concept: Optional #2913

Are you sure you want to change the base?

New concept: Optional #2913

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