Edge.java

public class Edge implements Comparable<Edge> { 

    private final int v;
    private final int w;
    private final double weight;

    public Edge(int v, int w, double weight) {
        if (v < 0) throw new IllegalArgumentException("vertex index must be a nonnegative integer");
        if (w < 0) throw new IllegalArgumentException("vertex index must be a nonnegative integer");
        if (Double.isNaN(weight)) throw new IllegalArgumentException("Weight is NaN");
        this.v = v;
        this.w = w;
        this.weight = weight;
    }

    public double weight() { return weight; }

    public int either() { return v; }

    public int other(int vertex) {
        if      (vertex == v) return w;
        else if (vertex == w) return v;
        else throw new IllegalArgumentException("Illegal endpoint");
    }

    @Override // returns zero if equal. Less than zero if this < that. Greater than zero if this > that.
    public int compareTo(Edge that) {
        return Double.compare(this.weight, that.weight);
    }

    public String toString() {
        return String.format("%d-%d %.5f", v, w, weight);
    }

  
}