I know that we can use TreeSet to sort Strings and numbers in an natural order. What if there is a Set of objects?
For example:
I have a Person class
{
private String firstName;
private String lastName;
private int age;
}
Set person = new TreeSet();
I want person sorted by firstName when I initialize person.
Both Comparable and Comparator work for you, but I suggest Comparator because it doesn't require you modify Person class, you only need the write an implementation class based on the sorting attribute, therefore Comparator is much more flexiable:
import java.util.Comparator;
public class FirstNameComparator implements Comparator<Person> {
@Override
public int compare(Person o1, Person o2) {
String name1 = o1.getFirstName();
String name2 = o2.getFirstName();
return name1.compareTo(name2);
}
}
//instantiate TreeSet instance with FirstNameComparator
Set<Person> ts = new TreeSet<>(new FirstNameComparator());
Collections.sort takes in a List, so that won't work with a Set. But, since OP is using TreeSet, there's a constructor that accepts a Comparator, which would work here.
Comparator because it doesn't require you modify Person class. There's nothing wrong with modifying a class that should have natural ordering. A much stronger argument is that a class like Person probably doesn't have a single natural order.
Person.
Comparableand Oracle's object ordering tutorial.