Copy Constructor in Rectangle Class

A copy constructor is a constructor with a single argument of the same type as the class. Making a copy of an object requires a special method called a copy constructor. The copy constructor should create an object that is a separate, independent object, but with the instance variables set so that it is an exact copy of the argument object.

You will create a copy constructor in the Rectangle class. Because of composition, you will have to create a copy constructor in the Point class and use it in the Rectangle class. Note that Point is immutable, so that the copy constructor in the Point class is not really necessary.

// copy constructor in Point class
public Point(Point original)
{
    // Add your code here
}

// copy constructor in Rectangle class, which
// will use the copy constructor in Point class
public Rectangle(Rectangle original)
{
    upperLeft = new Point(original.upperLeft)
	// Finish the rest of the code for another
    // three instance variables
}

Note that the following copy constructor is COMPLETELY WRONG:


public Rectangle(Rectangle original)
{
    upperLeft = original.upperLeft;
}

This is called aliasing. What this WRONG constructor is doing is setting the pointer to upperLeft equal to the pointer to the original Rectangle's upperLeft, like so:

With this WRONG constructor, every time the original's upperLeft changes, our new object's upperLeft will change as well.

Testing

Uncomment the last part of the test program in main. Use the same test case as in step 5 to test your program.

  Scanner scanner = new Scanner(System.in);
  int x = 1;
  int y = 1;

  System.out.print("Enter the coordinates of the upperLeft point (x y):");
  x = scanner.nextInt();
  y = scanner.nextInt();

  Point upperLeft = new Point(x, y);

  
  System.out.print("Enter the coordinates of the lowerLeft point (x y):");
  x = scanner.nextInt();
  y = scanner.nextInt();

  Point lowerLeft = new Point(x, y);
  
  
  System.out.print("Enter the coordinates of the lowerRight point (x y):");
  x = scanner.nextInt();
  y = scanner.nextInt();

  Point lowerRight = new Point(x, y);
  
  
  System.out.print("Enter the coordinates of the upperRight point (x y):");
  x = scanner.nextInt();
  y = scanner.nextInt();

  Point upperRight = new Point(x, y);
  
  Rectangle rectangle = new Rectangle(upperLeft, lowerLeft, lowerRight, upperRight);

  System.out.printf("Length of rectangle : %.2f\n", rectangle.getLength());
  System.out.printf("Width of rectangle : %.2f\n", rectangle.getWidth());
  System.out.printf("Area of rectangle : %.2f\n", rectangle.getArea());
  System.out.printf("Perimeter of rectangle : %.2f\n", rectangle.getPerimeter());

  //test the copy constructor
  Rectangle rectangleNew = new Rectangle(rectangle);
  
  System.out.printf("Length of rectangleNew : %.2f\n", rectangleNew.getLength());
  System.out.printf("Width of rectangleNew : %.2f\n", rectangleNew.getWidth());
  System.out.printf("Area of rectangleNew : %.2f\n", rectangleNew.getArea());
  System.out.printf("Perimeter of rectangleNew : %.2f\n", rectangleNew.getPerimeter());

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CMSC 202 — Spring 2012

Copy Constructor in Rectangle Class

Testing