polyline.java

JAVA 2入门经典 练习答案

// Chapter 6 Exercise 6

// Modified to iterate through the points and insert and delete points:

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.
    	}
   }

   // Get the first point:    
   public Point getFirst() {
      	return (Point)polyline.getFirst();
   }

   // Get the next point after current:    
   public Point getNext() {
      	return (Point)polyline.getNext();
   }

   // Insert a point after current:          
   public void insert(Point point) {
      	polyline.insert(point);
   }
    
   // Delete the current point:                            
   void delete() {
      	polyline.delete();
   }

   // Method to insert point after the Point, position: 
   public boolean insert(Point point, Point position) {
      return polyline.insert(point, position);
   }
}