Organize list based on an integer value of its elements

Question

I have a ArrayList of a class of mine that contains variables String and integers, as a name and punctuation. When I display it through a Adapter I would like the list to be in descending order, but I couldn’t find how to do it. Does anyone know how? In case the text is the name the score is the approval of the comment.

Below is the part where I create the list and display it:

public class F_ListaComentarios extends ListFragment {

    C_Comentario comentario;
    private List<C_Comentario> comentarios;

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        comentarios = new ArrayList<C_Comentario>();

        preencherListaComentarios(comentarios);

        if (comentarios != null) {
            adapter = new P_ComentarioAdapter(getActivity(), comentarios);
            setListAdapter(adapter);
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.f_lista_comentarios, null, false);
        return (view);
    }

    public void preencherListaComentarios(ArrayList<C_Comentario> comentarios) {

        C_Comentario comentario = new C_Comentario();
        comentario.setTexto("AA");
        comentario.setAprovado(0);
        comentarios.add(comentario);

        C_Comentario comentario2 = new C_Comentario();
        comentario.setTexto("AV");
        comentario.setAprovado(2);
        comentarios.add(comentario);

        C_Comentario comentario3 = new C_Comentario();
        comentario.setTexto("AA");
        comentario.setAprovado(1);
        comentarios.add(comentario);

        C_Comentario comentario4 = new C_Comentario();
        comentario.setTexto("AA");
        comentario.setAprovado(5);
        comentarios.add(comentario);
    }
}

I managed to solve by implementing Comparable<C_Comentario> to my class C_Comentario and adding

public static final Comparator<C_Comentario> DESCENDING_COMPARATOR = new Comparator<C_Comentario>() {
        // Overriding the compare method to sort the age
        public int compare(C_Comentario c, C_Comentario c1) {
            return c1.aprovado - c.aprovado;
        }
    };

e

@Override
    public int compareTo(C_Comentario c) {
        return (this.titulo).compareTo(c.titulo);
    }
}

the class also.

In the fragment I just had to call

Collections.sort(comentarios, C_Comentario.DESCENDING_COMPARATOR);

Answer 1

Use the method Collections.sort() passing as argument their ArrayList and an object Comparator<T>. The very Collections provides the Collections.reverseOrder.

import java.util.ArrayList;
import java.util.Collections;

// ...
ArrayList<Integer> lista = new ArrayList<>();
lista.add(432);
lista.add(23);
lista.add(18);
lista.add(2);
lista.add(100);

Collections.sort(lista, Collections.reverseOrder());
System.out.println(lista); // [432, 100, 23, 18, 2]

---

Example working on Ideone