Sorting a List of Objects in Java: A Configurable Approach with Comparator and Enums

In this article, I have shown a way to sort a list of Employee object based on a specific field and the sorting order using Comparator. The code snippet shows that the sorting criteria are configurable, eliminating the need to add an if/else block when a new criterion is introduced.

class Employee {
    private int ID;
    private String name;
    private String age;
    public int getID() {
        return ID;
    }

    public void setID(int ID) {
        this.ID = ID;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAge() {
        return age;
    }

    public void setAge(String age) {
        this.age = age;
    }
}

Create two enums SortingCriteria and SortingOrder.

enum SortingCriteria {
    NAME, AGE
}
enum SortingOrder {
ASC, DESC
}

Now create a Map to store SortingCriteria mapping with the ascending order (default) Comparators e.g., Name comparator, Age comparator, etc.

    static Map<SortingCriteria, Comparator<Employee>> comparatorMap = Map.of(NAME, Comparator.comparing(Employee::getName), AGE, Comparator.comparing(Employee::getAge));

Create a method to accept the SortingCriteria and the SortingOrder as user input and return the sorted employees. Here we are assuming that a List of employees is already available.

 static List<Employee> sort(SortingCriteria criteria, SortingOrder order) {
        List<Employee> employees = new ArrayList<>(); // consider populated
        //If order is DESC then we take reversed() comparator
        Comparator<Employee> employeeComparator = order == ASC ? comparatorMap.get(criteria) : comparatorMap.get(criteria).reversed();
        employees.sort(employeeComparator);
        return employees;
    }

Conclusion: The benefit of this approach is that to enable sorting for a new criterion, let's say ID, we just need to add ID in SortingCriteria and add a new mapping in the comparatorMap. This way, the core sorting logic remains unchanged.