Sorting using Comparator- Descending order (User defined classes) [closed]

Question

I want to sort my objects in descending order using comparator.

class Person {  private int age; } 

Here I want to sort a array of Person objects.

How can I do this?

Answer 1

You can do the descending sort of a user-defined class this way overriding the compare() method,

Collections.sort(unsortedList,new Comparator<Person>() {     @Override     public int compare(Person a, Person b) {         return b.getName().compareTo(a.getName());     } }); 

Or by using Collection.reverse() to sort descending as user Prince mentioned in his comment.

And you can do the ascending sort like this,

Collections.sort(unsortedList,new Comparator<Person>() {     @Override     public int compare(Person a, Person b) {         return a.getName().compareTo(b.getName());     } }); 

Replace the above code with a Lambda expression(Java 8 onwards) we get concise:

Collections.sort(personList, (Person a, Person b) -> b.getName().compareTo(a.getName())); 

As of Java 8, List has sort() method which takes Comparator as parameter(more concise) :

personList.sort((a,b)->b.getName().compareTo(a.getName())); 

Here a and b are inferred as Person type by lambda expression.