Question

I’ve got following array:

private static Optreden[] optredens = {
            new Optreden("Editors", "Main Stage", 16, 0, 4),
            new Optreden("Empire of the Sun", "Pyramid Marquee", 23, 45, 5),
            new Optreden("Florence and the Machine", "Marquee", 18, 45, 3),
            new Optreden("The Specials", "Marquee", 13, 10, 5),
            new Optreden("Muse", "Main Stage", 19, 0, 5),
            new Optreden("Faithless", "Main Stage", 14, 30, 5),
            new Optreden("Absynthe Minded", "Pyramid Marquee", 21, 45, 5),
            new Optreden("Pink", "Main Stage", 20, 30, 2),
            new Optreden("Editors", "Marquee", 21, 20, 4),
            new Optreden("Faithless", "Pyramid Marquee", 19, 0, 5)
            };

The Optreden object constructor looks like this:

Optreden(name, stage, hour, minutes, rating);

Now, I have to create a HashSet of the Optreden objects BUT it may not contain duplicate names, so when I print the HashSet it has to look like this:

The Specials (Marquee, 13u10)--> *****
Empire of the Sun (Pyramid Marquee, 23u45)--> *****
Florence and the Machine (Marquee, 18u45)--> ***
Pink (Main Stage, 20u30)--> **
Muse (Main Stage, 19u)--> *****
Absynthe Minded (Pyramid Marquee, 21u45)--> *****
Editors (Main Stage, 16u)--> ****
Faithless (Main Stage, 14u30)--> *****

Thing is, I can’t edit the Optreden class and it only has a constructor and a toString method, no getName() getter.

How can I pull this off? Thanks.

Answer 1

As long as Optreden is not a final class, you can subclass it to trap name in the constructor and implement equals() and hashcode() to use name, as follows:

public class MyOptreden extends Optreden
{
    private String name;

    public MyOptreden(String name, String stage, int hour, int minutes, int rating) {
        super(name, stage, hour, minutes, rating);
        this.name = name; // A capture name here
    }

    @Override
    public boolean equals(Object obj) {
        return obj instanceof MyOptreden && ((MyOptreden) obj).name.equals(name);
    }

    @Override
    public int hashCode() {
        return name.hashCode();
    }
}

As long as you are using only instances of this class in your set, it will work.

You will have to override setName(), if it exists, to update name.