Quaternion Comparison?

Is quaternion comparison possible? I'm writing a Java class of Quaternions and I want to implement the Comparable interface to use the Collections.sort(List) facility. I'm not expert at math, I really don't understand the things I read about Quaternions. So, can anyone tell me can I override the compareTo method for Quaternions and how?

My class declarition:

public class Quaternion implements Serializable, Comparable {

    private double s; // scalar part
    private double i, j, k; // vectorel part


    public Quaternion() {
        super();
    }

    public Quaternion(double s, double i, double j, double k) {
        super();
        this.s = s;
        this.i = i;
        this.j = j;
        this.k = k;
    }