trypolyline.java

JAVA 2入门经典 练习答案

// Chapter 6 Exercise 6

public class TryPolyLine {
   public static void main(String[] args) {
      // Create an array of coordinate pairs:
      double[][] coords = { {1., 1.}, {1., 2.}, { 2., 3.},
                            {-3., 5.}, {-5., 1.}, {0., 0.} };

      // Create a polyline from the coordinates and display it:
      PolyLine polygon = new PolyLine(coords);
      polygon.show();

      // Add a point and display the polyline again:
      polygon.addPoint(10., 10.);
      polygon.show();

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

      // Use the points to create a new polyline and display it:
      PolyLine newPoly = new PolyLine(points);
      newPoly.show();

      // Count the number of points:
      Point point = newPoly.getFirst();
      int count = 0;
      while(point != null) {
        count++;
        point = newPoly.getNext();
      }
      System.out.println("\nPolyline has " + count + " points."+
                         " Inserting a point after point number " + (count/2));

      int insertCount = count/2;
      point = newPoly.getFirst();
      while(--insertCount>0)
        point = newPoly.getNext();
      System.out.println("\nCurrent point is " + point);

      newPoly.insert(new Point(99.0,99.0));          // Insert a point.      
      newPoly.show();                                // Output the polyline.

      if(newPoly.insert(new Point(88.0, 88.0), new Point(99.0, 99.0)))
       System.out.println("\nInsertion after a given point successful.");
      else
       System.out.println("\nInsertion after a given point failed.");
      newPoly.show();                                // Output the polyline.

      // Now delete the first point we inserted:
      int deleteCount = 1 + count/2;                 // Count to position of point.     

      // Go to the point we want to delete:
      point = newPoly.getFirst();
      while(--deleteCount>0)
        point = newPoly.getNext();
      System.out.println("\nDeleting the current point which is " + point);

      newPoly.delete();                              // Delete the point.
      newPoly.show();                                // Output the polyline.
   }
}