DirectedEdge.java

/******************************************************************************
 *  Compilation:  javac DirectedEdge.java
 *  Execution:    java DirectedEdge
 *  Dependencies: StdOut.java
 *
 *  Immutable weighted directed edge.
 *
 ******************************************************************************/
/**
 * The {@code DirectedEdge} class represents a weighted edge in an
 * {@link EdgeWeightedDigraph}. Each edge consists of two integers (naming the
 * two vertices) and a real-value weight. The data type provides methods for
 * accessing the two endpoints of the directed edge and the weight.
 * <p>
 * For additional documentation, see
 * <a href="https://algs4.cs.princeton.edu/44sp">Section 4.4</a> of
 * <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
 *
 * @author Robert Sedgewick
 * @author Kevin Wayne
 */

public class DirectedEdge implements Comparable<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 non-negative integers");
		if (w < 0)
			throw new IllegalArgumentException("Vertex names must be non-negative 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);
	}

	/**
	 * Unit tests the {@code DirectedEdge} data type.
	 *
	 * @param args
	 *            the command-line arguments
	 */
	public static void main(String[] args)
	{
		DirectedEdge e = new DirectedEdge(12, 34, 5.67);
		System.out.println(e);
	}

	@Override
	public int compareTo(DirectedEdge o)
	{
		// TODO Auto-generated method stub
		return v -o.v;
	}
}