public class Edge implements Comparable<Edge> {

    //...

    @Override
    public int compareTo(Edge edge) {
        double w1 = this.getWeight();
        double w2 = edge.getWeight();
        if (w1 < w2){
            return -1;
        } else if (w1 == w2){
            return 0;
        } else {
            return 1;
        }
    }

}