How Can I Flexibly Sort Lists of Objects by Different Properties?

Easily Sorting Collections of Objects

Question:

When working with lists of objects (e.g., Person), how can we flexibly sort by different properties (e.g., name, age, or country)?

Answer:

While the Comparable interface allows sorting by a single property, a more versatile approach is to use custom comparators with the Collections.sort method. An example for sorting a Person class:

public class FlexiblePersonComparator implements Comparator<Person> {
    public enum Order { Name, Age, Country }

    private Order sortingBy = Order.Name;

    @Override
    public int compare(Person person1, Person person2) {
        switch (sortingBy) {
            case Name:
                return person1.name.compareTo(person2.name);
            case Age:
                return person1.age.compareTo(person2.age);
            case Country:
                return person1.country.compareTo(person2.country);
        }
        throw new RuntimeException("Practically unreachable code, can't be thrown");
    }

    public void setSortingBy(Order sortBy) {
        this.sortingBy = sortBy;
    }
}

Utilizing the comparator:

public void sortPersonsBy(FlexiblePersonComparator.Order sortingBy) {
    List<Person> persons = this.persons;  // Useless line for clarification
    FlexiblePersonComparator comparator = new FlexiblePersonComparator();
    comparator.setSortingBy(sortingBy);
    Collections.sort(persons, comparator); // Sorting the list
}

By utilizing custom comparators, you gain the flexibility to sort collections of objects by any desired property, providing a convenient and versatile solution for sorting complex data structures.

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