DirectedEdge.java

package cas2xb3.greenlight;

public class DirectedEdge {
	private final int v;
	private final int w;
	private final double weight;

	/**
	 * Initializes a directed edge from vertex {@code v} to vertex {@code w}
	 * with the given {@code weight}.
	 * 
	 * @param v
	 *            the tail vertex
	 * @param w
	 *            the head vertex
	 * @param weight
	 *            the weight of the directed edge
	 * @throws IllegalArgumentException
	 *             if either {@code v} or {@code w} is a negative integer
	 * @throws IllegalArgumentException
	 *             if {@code weight} is {@code NaN}
	 */
	public DirectedEdge(int v, int w, double weight) {
		if (v < 0)
			throw new IllegalArgumentException("Vertex names must be nonnegative integers");
		if (w < 0)
			throw new IllegalArgumentException("Vertex names must be nonnegative integers");
		if (Double.isNaN(weight))
			throw new IllegalArgumentException("Weight is NaN");
		this.v = v;
		this.w = w;
		this.weight = weight;
	}

	/**
	 * Returns the tail vertex of the directed edge.
	 * 
	 * @return the tail vertex of the directed edge
	 */
	public int from() {
		return v;
	}

	/**
	 * Returns the head vertex of the directed edge.
	 * 
	 * @return the head vertex of the directed edge
	 */
	public int to() {
		return w;
	}

	/**
	 * Returns the weight of the directed edge.
	 * 
	 * @return the weight of the directed edge
	 */
	public double weight() {
		return weight;
	}

	/**
	 * Returns a string representation of the directed edge.
	 * 
	 * @return a string representation of the directed edge
	 */
	public String toString() {
		return v + "->" + w + " " + String.format("%5.2f", weight);
	}

}