testshapelist.java

JAVA 2入门经典 练习答案

// Chapter 6 Exercise 3

// Tests the operation of the ShapeList class.

public class TestShapeList {
  public static void main(String args[]) {
    ShapeList shapes = null;	           // Stores a shape list.
    Shape shape = null;                  // Stores a shape.
    int shapeCount = 10;                 // Number of shapes.
    Point[] pts;			                   // Declare a variable referencing an array of points.
    Point pt1 = null;                    // First working Point store.
    Point pt2 = null;			               // Second working Point store.
    double minRadius = 2.0;		           // Minimum radius of a circle.
    double maxRadius = 20.0;		         // Maximum radius of a circle.
    double maxDist = 100.0;		           // Maximum x,y coordinate value
    int minPts = 2;			                 // Minimum number of points in PolyLines.
    int maxPts = 15;                     // Maximum number of points in PolyLines.
    int choice;                          // Selector for shape type.

    for(int i=0;i<shapeCount;i++) {					 
      // Generate one of four random shapes:
      choice = (int)(4.0*Math.random()); 	// Shape choice 0 to 3.

      // Coordinates are cast to int just to make the output less messy.
      // The compiler will arrange to cast the integer arguments back to double.
      switch(choice) {
	      case 0:				 	// Generate a Line:
          // Generate two random points:
	        pt1 = new Point((int)(Math.random()*maxDist),(int)(Math.random()*maxDist));	
	        pt2 = new Point((int)(Math.random()*maxDist),(int)(Math.random()*maxDist));
	        shape = new Line(pt1,pt2); 
	        break;

	      case 1:					// Generate a Circle:
	        pt1 = new Point((int)(Math.random()*maxDist),(int)(Math.random()*maxDist));	
	        shape = new Circle(pt1, (int)(minRadius+(maxRadius-minRadius)*Math.random()));
	        break;

	      case 2:					// Generate a Rectangle:
          // Generate two random points
	        pt1 = new Point((int)(Math.random()*maxDist),(int)(Math.random()*maxDist));	
	        pt2 = new Point((int)(Math.random()*maxDist),(int)(Math.random()*maxDist));
	        shape = new Rectangle(pt1,pt2);	
	        break;

	      case 3:					// Generate a PolyLine:
          // Create a Point array with a random number of elements:
	        pts = new Point[minPts+(int)((maxPts-minPts)*Math.random())];

          // Fill array with random points:
	        for(int j=0;j<pts.length;j++)
	          pts[j] = new Point((int)(Math.random()*maxDist),(int)(Math.random()*maxDist));

	        shape = new PolyLine(pts);	 	// Create a PolyLine.
	        break;

        default:                               	// We should never get to here.
          System.out.println("\nInvalid shape choice = "+choice);
          System.exit(1);
          break;
      }
      if(shapes == null)
        shapes = new ShapeList(shape);
      else
        shapes.add(shape);
    }

    // Output all the shapes in the Shape array:
    shapes.show();
  }
}