Sorting a collection using fluent chaining in Java 8

Question

Given a class.

public class Entity {

    private Long id;
    private String prodName;
    private BigDecimal price;

    // Constructors + getters + setters + hashcode() + equals() + toString().
}

Constructing a list of Entity.

List<Entity> list = new ArrayList<>();

Entity entity = new Entity();
entity.setId(1L);
entity.setProdName("A");
entity.setPrice(new BigDecimal(10));
list.add(entity);

entity = new Entity();
entity.setId(2L);
entity.setProdName("B");
entity.setPrice(new BigDecimal(20));
list.add(entity);

entity = new Entity();
entity.setId(3L);
entity.setProdName("C");
entity.setPrice(new BigDecimal(30));
list.add(entity);

entity = new Entity();
entity.setId(4L);
entity.setProdName("D");
entity.setPrice(new BigDecimal(40));
list.add(entity);

entity = new Entity();
entity.setId(5L);
entity.setProdName("E");
entity.setPrice(new BigDecimal(50));
list.add(entity);

entity = new Entity();
entity.setId(6L);
entity.setProdName("F");
entity.setPrice(new BigDecimal(60));
list.add(entity);

entity = new Entity();
entity.setId(7L);
entity.setProdName("F");
entity.setPrice(new BigDecimal(60));
list.add(entity);

Attempting to sort the list in descending order by price and prodName and then in ascending order by id.

Comparator<Entity> comparator = Comparator.comparing(Entity::getPrice).reversed();
comparator = comparator.thenComparing(Entity::getProdName).reversed();
comparator = comparator.thenComparingLong(Entity::getId);

list = list.stream().sorted(comparator).collect(Collectors.toList());
// Or Collections.sort(list, comparator);
list.stream().forEachOrdered(l -> System.out.println(l.getId() + " : " + l.getPrice() + " : " + l.getProdName()));

After performing sorting, the list should appear like the following.

6 : 60 : F
7 : 60 : F
5 : 50 : E
4 : 40 : D
3 : 30 : C
2 : 20 : B
1 : 10 : A

But the list, after sorting is performed, appears as follows.

1 : 10 : A
2 : 20 : B
3 : 30 : C
4 : 40 : D
5 : 50 : E
6 : 60 : F
7 : 60 : F

The sorted list is not according to the given criteria (descending order by price and prodName and ascending order by id).

What more needs to be done?

Answer 1

You're reversing the whole comparator every time you call reversed(). Instead, just do as your description says:

Comparator<Entity> comparator = Comparator.comparing(Entity::getPrice,
                                                     Comparator.reverseOrder());
comparator = comparator.thenComparing(Entity::getProdName, 
                                      Comparator.reverseOrder());
comparator = comparator.thenComparingLong(Entity::getId);

list = list.stream().sorted(comparator).collect(Collectors.toList());
list.stream().forEachOrdered(l -> System.out.println(l.getId() + " : " + l.getPrice() + " : " + l.getProdName()));