EmployeeRecordManager.java

import java.util.HashMap;
import java.util.Map;

// 1. Define the Employee Record
// Records automatically provide a constructor, getters (id(), name(), department()), 
// equals(), hashCode(), and toString() without any boilerplate code!
record Employee(int id, String name, String department) {
}

// 2. Main Driver Class (PascalCase)
public class EmployeeRecordManager {
    
    // Using a Map to store and manage the records. The ID is the Key, the Record is the Value.
    private Map<Integer, Employee> employeeDatabase;

    public EmployeeRecordManager() {
        employeeDatabase = new HashMap<>();
    }

    // Method to add a new employee to the Map
    public void addEmployee(Employee emp) {
        employeeDatabase.put(emp.id(), emp);
        System.out.println("Added: " + emp);
    }

    // Method to find an employee by their ID
    public Employee findEmployeeById(int id) {
        return employeeDatabase.get(id); // Returns the record, or null if not found
    }

    // Method to update the department of an employee
    public void updateDepartment(int id, String newDepartment) {
        Employee existingEmp = findEmployeeById(id);
        
        if (existingEmp != null) {
            // CRITICAL CONCEPT: Records are immutable! 
            // We cannot change the existing object. We must create a new record 
            // instance with the updated data and replace the old one in the Map.
            Employee updatedEmp = new Employee(existingEmp.id(), existingEmp.name(), newDepartment);
            
            employeeDatabase.put(id, updatedEmp); // Replaces the old record at this ID key
            System.out.println("Successfully updated department for ID " + id + " to '" + newDepartment + "'.");
        } else {
            System.out.println("Error: Employee with ID " + id + " not found in the database.");
        }
    }

    // Helper method to display all current employees
    public void displayAll() {
        System.out.println("\n--- Current Employee Database ---");
        if (employeeDatabase.isEmpty()) {
            System.out.println("No records found.");
        } else {
            for (Employee emp : employeeDatabase.values()) {
                System.out.println(emp);
            }
        }
        System.out.println("---------------------------------\n");
    }

    public static void main(String[] args) {
        System.out.println("--- Employee Record Management System ---");
        EmployeeRecordManager manager = new EmployeeRecordManager();

        // 1. Adding initial records
        manager.addEmployee(new Employee(101, "Alice Smith", "Engineering"));
        manager.addEmployee(new Employee(102, "Bob Jones", "Marketing"));
        manager.addEmployee(new Employee(103, "Charlie Brown", "Human Resources"));

        manager.displayAll();

        // 2. Finding an employee by ID
        System.out.println("Searching for Employee ID 102...");
        Employee found = manager.findEmployeeById(102);
        if (found != null) {
            System.out.println("Found: " + found);
        } else {
            System.out.println("Employee not found.");
        }

        // 3. Updating an employee's department
        System.out.println("\nUpdating Department for Employee ID 101...");
        manager.updateDepartment(101, "Research and Development");

        // 4. Display all again to verify the update worked
        manager.displayAll();
    }
}