Arraylist Comparator JSP Object

Question

I’m having trouble implementing the Comparator method, to sort the Object Arraylist.

I have an Enterprise class. Where I then create an Arraylist, which is filled from a content manager system.

I added the method compareTo, and it sorts by the Area attribute. But now I also need you to sort by number of rooms, and bathrooms.

How could I do that ?

Here is the current cider:

    <%! 
public class Empreendimento implements Comparable<Empreendimento>{

     //possui atributos, gets, sets e construtor

        public int compareTo(Empreendimento Emp) {
            if (this.menorArea < Emp.getMenorArea()) {
                return -1;
            }
            if (this.menorArea > Emp.getMenorArea()) {
                return 1;
            }
            return 0;
        }
%>

After the content manager, create the Arraylist with these obejtos. I make a filter, and then I order. Then I use this:

Collections.sort(ArrayResultadoBusca);

Answer 1

With Java 8, there is a simple and clean solution to handle multiple comparisons.

Lambda:

Comparator<Empreendimento> comparator = Comparator
        .comparing(e -> e.getMenorArea)
        .thenComparingInt(e -> e.getQuantidadeQuarto)
        .thenComparingInt(e -> e.getQuantidadeBanheiro);

Method Reference:

Comparator<Empreendimento> comparator = Comparator
        .comparing(Empreendimento::getMenorArea)
        .thenComparingInt(Empreendimento::getQuantidadeQuarto)
        .thenComparingInt(Empreendimento::getQuantidadeBanheiro);

It is not recommended to mix code html of view coded Java, it is interesting to make the comparison in a class and then pass the result by a Expression Language (EL).

An alternative is to implement a Comparator that instead of passing the attributes by parameter, passes two classes of the same type and compares their attributes.

Ex:

Collections.sort(lista, new Comparator<Empreendimento>(){
    public int compare(Empreendimento e1, Empreendimento e2) {
        int comparacao = e1.getMenorArea().compareTo(e2.getMenorArea());
        if(comparacao != 0) {
           return comparacao;
        }

        comparacao = e1.getQuantidadeQuarto().compareTo(e2.getQuantidadeQuarto());
        if(comparacao != 0) {
           return comparacao;
        }

        return e1.getQuantidadeBanheiro().compareTo(e2.getQuantidadeBanheiro());     
    }
});

It is important to implement the equals and hashCode in the model class, in that case Entrepreneurship.