How to compare objects by multiple fields

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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);
}

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