Let's start by discussing the methods we will implement in our EmployeeRecords
class.
addProject(employeeId: String, projectName: String): Boolean
— This method adds a new project to an employee's list of projects. If the project already exists for that employee, the method returnsfalse
. Otherwise, it adds the project and returnstrue
.addTask(employeeId: String, projectName: String, task: String): Boolean
— This method adds a new task to a specified project for an employee. If the project does not exist for that employee, the method returnsfalse
. If the task is added successfully, it returnstrue
.getTasks(employeeId: String, projectName: String): List<String>?
— This method retrieves all tasks for a specified project of an employee. If the project does not exist for that employee, the method returnsnull
. Otherwise, it returns the list of tasks.
Let's build our EmployeeRecords
class step-by-step, ensuring we understand each component clearly.
We'll start with the basic structure of the class and initialize our data storage.
Kotlin1class EmployeeRecords { 2 private val records: MutableMap<String, MutableMap<String, MutableList<String>>> = mutableMapOf() 3} 4 5fun main() { 6 val records = EmployeeRecords() 7}
In this initial setup, we define the EmployeeRecords
class and create a property records
that is a MutableMap
. Each key is an employee ID with a corresponding value being another map that holds projects and tasks.
Next, we'll implement the addProject
method to add projects to an employee's record.
Kotlin1class EmployeeRecords { 2 /* Other methods and properties omitted for brevity */ 3 4 fun addProject(employeeId: String, projectName: String): Boolean { 5 val employeeProjects = records.getOrPut(employeeId) { mutableMapOf() } 6 if (projectName in employeeProjects) { 7 return false 8 } else { 9 employeeProjects[projectName] = mutableListOf() 10 return true 11 } 12 } 13} 14 15fun main() { 16 val records = EmployeeRecords() 17 println(records.addProject("E123", "ProjectA")) // Returns true 18 println(records.addProject("E123", "ProjectA")) // Returns false 19}
Here, the addProject
method uses getOrPut
to check if the given employeeId
exists in the records
map. This method creates an empty map for an employee if none exists. It checks if the projectName
already exists, returning false
if it does. Otherwise, it creates a new empty list for tasks and returns true
.
Now, we will implement the addTask
method, which depends on the existence of the project.
Kotlin1class EmployeeRecords { 2 /* Other methods and properties omitted for brevity */ 3 4 fun addTask(employeeId: String, projectName: String, task: String): Boolean { 5 val employeeProjects = records[employeeId] 6 val tasks = employeeProjects?.get(projectName) 7 return if (tasks != null) { 8 tasks.add(task) 9 true 10 } else { 11 false 12 } 13 } 14} 15 16fun main() { 17 val records = EmployeeRecords() 18 records.addProject("E123", "ProjectA") 19 println(records.addTask("E123", "ProjectA", "Task1")) // Returns true 20 println(records.addTask("E123", "NonExistentProject", "Task2")) // Returns false 21}
The addTask
method first tries to obtain the list of tasks for the specified project. If the employee or project doesn't exist, the method returns false
. Otherwise, it appends the task to the list and returns true
.
Lastly, let's implement the getTasks
method to retrieve tasks from a specified employee's project.
Kotlin1class EmployeeRecords { 2 /* Other methods and properties omitted for brevity */ 3 4 fun getTasks(employeeId: String, projectName: String): List<String>? { 5 return records[employeeId]?.get(projectName) 6 } 7} 8 9fun main() { 10 val records = EmployeeRecords() 11 records.addProject("E123", "ProjectA") 12 records.addTask("E123", "ProjectA", "Task1") 13 println(records.getTasks("E123", "ProjectA")) // Returns ["Task1"] 14 println(records.getTasks("E123", "NonExistentProject")) // Returns null 15}
The getTasks
method attempts to retrieve the list of tasks for the specified project. If it doesn't exist, null
is returned. Otherwise, the list of tasks is returned.
In this lesson, we successfully implemented the EmployeeRecords
class for managing projects and tasks for employees using Kotlin's MutableMap
and MutableList
. We covered methods for adding projects, adding tasks to those projects, and retrieving tasks from those projects.
Understanding how to work with Kotlin's collections and effectively handle nullable types will enhance your ability to manage complex data hierarchies. Continue practicing with these concepts to further build your skills.
Keep coding and exploring new challenges!