Sorting objects of a class

Question

I'm working on a Java project that asks me to implement the function obtainRanking() : void with the following description:

Sort the players list by using the class method sort (List) from the Collections class, a method to sort the objects of a collection. For that, the object's class (Player in our case), should implement the interface "Comparable" and its method compareTo.

So far, this is how I implemented the interface Comparable:

package modeloqytetet;

public interface Comparable {
    public int compareTo(Object otroJugador);
}

Inside class Player this is how I implemented the said method:

@Override
    public int compareTo(Object otherJugador) {
        int otherCapital = ((Player) otherJugador).getCapital();

        return otherCapital-getCapital();
    }

Now, the method obtainRanking() : void should be implemented in other class and I don't know how to do it. I've been trying to figure out by looking some examples around the internet but nothing seems to work.

Any help would be appreciated.

Answer 1

The instructions is telling you to implement java.lang.Comparable<T>, not your own Comparable interface.

You should do this:

class Player implements Comparable<Player> {
    @Override
    public int compareTo(Player other) {
        return Integer.compare(this.getCapital(), other.getCapital());
    }

    ...
}

For why you should not simply subtract one integer from another to compare them, see here.

Then, you can implement obtainRankings like this:

// this name is quite bad. I would call it sortPlayersCapitalInPlace or something like that
public void obtainRankings(List<Player> players) {
    Collections.sort(players);
}