With Java 8 we can use a lambda expression to implement a Comparator for sorting a collection:

class Person {
    public String name;
    public int age;

// TODO we should add some persons to this list
List<Person> persons = new ArrayList<>();

// Using a lambda expression to implement the Comparator
Collections.sort(persons, (p1, p2) -> p1.name.compareTo(p2.name));

Before Java 8, we had to write code like this:

Collections.sort(persons, new Comparator<Person>() {
    public int compare(Person p1, Person p2) {
        return p1.name.compareTo(p2.name);