What is a typeclass?

If you’ve used Java a reasonable amount there’s a prime candidate of how we do things with inheritance:

public interface Comparable<T> {
    public int compareTo(T o);
}

Later on in Java we got this as an alternative:

public interface Comparator<T> {
    int compare(T o1, T o2);
}

The above is probably the closest Java has to typeclasses.