On a single diagram, illustrate the following using the UML notation for objects, links and messages.
(a) An object of class Window, with no attributes shown;
(b) An object of class Rectangle with attributes length and width. Assume that the Rectangle class supports an operation to return the area of a rectangle object.
(c) A link between the window and rectangle objects, modeling the fact that the rectangle defines the screen co-ordinates of the window.
(d) The window object sending a message to the rectangle asking for its area.
Draw a class diagram showing Window and Rectangle classes with the properties mentioned in this question.