polyline.java

Beginning Java 2, SDK 1.4 Edition Exercise Code samples for this book

// Chapter 6 Exercise 4

// This has been modified to output the point in reverse order
// to test the new LinkedList capability for traversing a list backwards

public class PolyLine {
  LinkedList polyline;      			// The linked list of points.

  // Construct a polyline from an array of coordinate pairs:
  public PolyLine(double[][] coords) {
    Point[] points = new Point[coords.length];  // Array to hold points.

    // Create points from the coordinates:
    for(int i = 0; i < coords.length ; i++)
      points[i] = new Point(coords[i][0], coords[i][1]);

    // Create the polyline from the array of points:
    polyline = new LinkedList(points); 
  }

  // Construct a polyline from an array of points:
  public PolyLine(Point[] points) {
    polyline = new LinkedList(points);      	// Create the polyline.
  }
  
  // Add a Point object to the list:
   public void addPoint(Point point) {
    polyline.addItem(point);                 	// Add the point to the list.
   }

  // Add a point from a coordinate pair to the list:
   public void addPoint(double x, double y) {
     polyline.addItem(new Point(x, y));    	 // Add the point to the list.
  }

  // Output the polyline in reverse order:
  public void show() {
    System.out.println("Polyline points are:");

    // Set the 1st point as start:
    Point nextPoint = (Point)polyline.getLast();                 //  ***   

    // Output the points:
    while(nextPoint != null) {
      System.out.println(nextPoint);             // Output the current point.
      nextPoint = (Point)polyline.getPrevious(); // Get the next point.
    }
  }
}