How do you sort a list of custom objects in Java?

public class Employee {
    private String name;
    private int age;
    private double salary;
    private String department;

    public Employee(String name, int age, double salary, String department) {
        this.name       = name;
        this.age        = age;
        this.salary     = salary;
        this.department = department;
    }

    // Getters
    public String getName()       { return name; }
    public int getAge()           { return age; }
    public double getSalary()     { return salary; }
    public String getDepartment() { return department; }

    @Override
    public String toString() {
        return name + "(" + age + ", $" + salary + ", " + department + ")";
    }
}

// Make Employee implement Comparable to define natural ordering
public class Employee implements Comparable<Employee> {
    // ... fields and getters ...

    @Override
    public int compareTo(Employee other) {
        return this.name.compareTo(other.name); // natural order = by name
    }
}

List<Employee> employees = Arrays.asList(
    new Employee("Charlie", 30, 75000, "QA"),
    new Employee("Alice",   25, 90000, "Dev"),
    new Employee("Bob",     28, 80000, "QA")
);

Collections.sort(employees);  // uses compareTo
employees.forEach(System.out::println);
// Alice(25, $90000.0, Dev)
// Bob(28, $80000.0, QA)
// Charlie(30, $75000.0, QA)

// Sort by salary ascending
employees.sort(Comparator.comparingDouble(Employee::getSalary));

// Sort by salary descending
employees.sort(Comparator.comparingDouble(Employee::getSalary).reversed());

// Sort by age ascending
employees.sort(Comparator.comparingInt(Employee::getAge));

// Sort by department, then by name within department
employees.sort(
    Comparator.comparing(Employee::getDepartment)
              .thenComparing(Employee::getName)
);

// Sort by salary descending, then age ascending
employees.sort(
    Comparator.comparingDouble(Employee::getSalary).reversed()
              .thenComparingInt(Employee::getAge)
);

// Sort alphabetically by name
employees.sort((e1, e2) -> e1.getName().compareTo(e2.getName()));

// Sort by salary descending (manual)
employees.sort((e1, e2) -> Double.compare(e2.getSalary(), e1.getSalary()));

// Returns NEW sorted list — doesn''t modify original
List<Employee> byName = employees.stream()
    .sorted(Comparator.comparing(Employee::getName))
    .collect(Collectors.toList());

// Find top 3 highest paid
List<Employee> top3 = employees.stream()
    .sorted(Comparator.comparingDouble(Employee::getSalary).reversed())
    .limit(3)
    .collect(Collectors.toList());

// Sort test data before comparison
List<String> actualProducts = getProductNamesFromUI();
List<String> expectedProducts = Arrays.asList("Laptop", "Mouse", "Keyboard");

Collections.sort(actualProducts);
Collections.sort(expectedProducts);
assertEquals(expectedProducts, actualProducts, "Product list mismatch");

// Verify dropdown is sorted
List<String> dropdownOptions = getDropdownOptions();
List<String> sortedExpected = new ArrayList<>(dropdownOptions);
Collections.sort(sortedExpected);
assertEquals(sortedExpected, dropdownOptions, "Dropdown not sorted alphabetically");