File "Element.java"

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import java.awt.*;
import java.io.Serializable;

import java.awt.geom.*;

public abstract class Element implements Serializable{
  public Element(Point position, Color color) {
    this.position = new Point(position);
    this.color = color;
  }

  // Returns the color of the element
  public Color getColor() {
    return color;
  }

  // Returns the position of the element
  public Point getPosition() {
    return position;
  }

  // Returns the bounding rectangle enclosing an element boundary
  public java.awt.Rectangle getBounds() {
    return bounds;
  }

  // Create a new element
  public static Element createElement(int type, Color color, Point start, Point end) {
	  
	  int LINE      = 101;
	  int RECTANGLE = 102;
	 int CIRCLE    = 103;
	 int CURVE     = 104;

	  // Initial conditions

    switch(type) {
      case 101:
        return new Element.Line(start, end, color);
      case 102:
         return new Rectangle(start, end, color);
      case 103:
//        return new Circle(start, end, color);
      case 104:
//        return new Curve(start, end, color);
      default:
       assert false;                     // We should never get to here
    }
    return null;
  }

  // Nested class defining a line
  public static class Line extends Element {
    public Line(Point start, Point end, Color color) {
      super(start, color);
      line = new Line2D.Double(origin.x, origin.y, end.x - position.x, end.y - position.y);
      bounds = new java.awt.Rectangle(
                     Math.min(start.x ,end.x),    Math.min(start.y, end.y),
                     Math.abs(start.x - end.x)+1, Math.abs(start.y - end.y)+1);
    }

    // Change the end point for the line
    public void modify(Point start, Point last) {
      line.x2 = last.x - position.x;
      line.y2 = last.y - position.y;
      bounds = new java.awt.Rectangle(
                   Math.min(start.x ,last.x),    Math.min(start.y, last.y),
                   Math.abs(start.x - last.x)+1, Math.abs(start.y - last.y)+1);
    }

    // Display the line
    public  void draw(Graphics2D g2D) {
     g2D.setPaint(color);                                              // Set the line color
     g2D.translate(position.x, position.y);                            // Move context origin
     g2D.draw(line);                                                   // Draw the line
     g2D.translate(-position.x, -position.y);                          // Move context origin back
    }
    private Line2D.Double line;
    private final static long serialVersionUID = 1001L;
  }

  // Nested class defining a rectangle
  public static class Rectangle extends Element {
    public Rectangle(Point start, Point end, Color color) {
      super(new Point(Math.min(start.x, end.x), Math.min(start.y, end.y)), color);
      rectangle = new Rectangle2D.Double(
        origin.x, origin.y,                                            // Top-left corner
        Math.abs(start.x - end.x), Math.abs(start.y - end.y));         // Width & height
      bounds = new java.awt.Rectangle(
                    Math.min(start.x ,end.x),    Math.min(start.y, end.y),
                    Math.abs(start.x - end.x)+1, Math.abs(start.y - end.y)+1);
    }

    // Display the rectangle
    public  void draw(Graphics2D g2D) {
      g2D.setPaint(color);                                             // Set the rectangle color
      g2D.translate(position.x, position.y);                           // Move context origin
      g2D.draw(rectangle);                                             // Draw the rectangle
      g2D.translate(-position.x, -position.y);                         // Move context origin back
    }

    // Method to redefine the rectangle
    public void modify(Point start, Point last) {
      bounds.x = position.x = Math.min(start.x, last.x);
      bounds.y = position.y = Math.min(start.y, last.y);
      rectangle.width = Math.abs(start.x - last.x);
      rectangle.height = Math.abs(start.y - last.y);
      bounds.width = (int)rectangle.width +1;
      bounds.height = (int)rectangle.height + 1;
    }

    private Rectangle2D.Double rectangle;
    private final static long serialVersionUID = 1001L;
  }

  // Abstract Element class methods
  public abstract void draw(Graphics2D g2D);
  public abstract void modify(Point start, Point last);

  // Element class fields
  protected Point position;                                            // Position of a shape
  protected Color color;                                               // Color of a shape
  protected java.awt.Rectangle bounds;                                 // Bounding rectangle
  protected static final Point origin = new Point();                   // Origin for elements
  private final static long serialVersionUID = 1001L;
}