Java Comparator using .reverseOrder() but with an inner class

Question

I am creating a simple program to learn about the Java Comparator class. I have sorted an Arraylist into order but now I want to sort the list in descending order b

Answer 1

Let's take a simple example we have a class Person with two fields name age and we want to sort an existing collection of persons based on their age so let's assume that we have a class Person with a constructor and add the persons into the list and then sort them unsing the method sort of collection :

Person bachiri = new Person (17,"bachiri");
Person taoufiq = new Person (14,"Taoufiq");
Person abderrahman = new Person (15,"abderrahman");
List persons =  new ArrayList<>();

and this this the impelemtation of Agecomparable :

class AgeComparator implements Comparator{


    @Override
    public int compare(Person person1, Person person2) {
        return Integer.compare(person1.getAge(),person2.getAge());
    }


}

the trick is to multiple the return method with -1 so the final result will be reversed: class AgeComparator implements Comparator{

    @Override
    public int compare(Person person1, Person person2) {
        return -1 * Integer.compare(person1.getAge(),person2.getAge());
    }


}

so now we can get a reversed result :

Collection.sort (Persons, new AgeComparator());