How to compare objects by multiple fields

Question

Assume you have some objects which have several fields they can be compared by:

public class Person {

    private String firstName;
    private String lastN         


        

Answer 1

With Java 8:

Comparator.comparing((Person p)->p.firstName)
          .thenComparing(p->p.lastName)
          .thenComparingInt(p->p.age);

If you have accessor methods:

Comparator.comparing(Person::getFirstName)
          .thenComparing(Person::getLastName)
          .thenComparingInt(Person::getAge);

If a class implements Comparable then such comparator may be used in compareTo method:

@Override
public int compareTo(Person o){
    return Comparator.comparing(Person::getFirstName)
              .thenComparing(Person::getLastName)
              .thenComparingInt(Person::getAge)
              .compare(this, o);
}