Design the Data Structures
By the end of this lesson, you'll be able to:
- Identify which collection type fits each piece of an employee management problem
- Sketch the data structures before writing implementation code
- Apply the collection decision process from Module 16 to a real scenario
Prerequisites: Module 16: "Collections: Sets and Maps"
What we're building
Over this module you'll build a small employee management system that:
- Stores employees in a directory, looked up by employee ID.
- Deduplicates and validates employee data using Sets.
- Generates reports (like headcount by department) from the underlying collections.
- Handles edge cases — a missing employee, invalid data — gracefully.
Each lesson builds one piece, reusing the collection and OOP patterns from Modules 10-16.
Applying the decision process
Using Module 16's three-question process on this problem:
- "Look up an employee by their employee ID." → Map (
Map<String, Employee>, direct key lookup). - "Track which departments exist, with no duplicates." → Set (
Set<String>, uniqueness only). - "List every employee in a specific department, in the order they were hired." → List (
List<Employee>, order matters).
Each of these was a plain "which collection?" question the moment the actual requirement was written out clearly — the same process from Module 16, just applied to real requirements instead of abstract examples.
Sketching before code
EmployeeDirectory
- holds: Map<String, Employee> keyed by employee ID
- responsible for: adding an employee, looking one up, listing all
department names (deduplicated)
Employee
- holds: employeeId, name, department, hireDate
- responsible for: describing itselfExactly the same "find the nouns, sketch responsibilities" approach from Module 12's "Design the Classes" lesson — now with the added step of naming which collection type each responsibility actually needs.
Exercise
As a comment, decide which collection type fits: "track every unique job title across all employees, order doesn't matter."
Show hint
Uniqueness matters, order doesn't.
Design the Data Structures Quiz
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Summary
Before writing any code, this lesson maps out which collection type — List, Set, or Map — fits each piece of an employee management system, using the decision process from Module 16.