DirectedEdge.java

Below is the syntax highlighted version of DirectedEdge.java from §4.4 Shortest Paths.

/******************************************************************************
 *  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 {
    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);
        StdOut.println(e);
    }
}