MSO Exam November 7, 2016, 13:30 15:30, Educ-Gamma

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1 MSO Exam November 7, 2016, 13:30 15:30, Educ-Gamma Name: Student number: Please read the following instructions carefully: Fill in your name and student number above. Be prepared to identify yourself with your student card when you submit your exam. This is a closed-book exam. You are forbidden from accessing any external material, notes, electronic material, or online resources. Answer each open question in the space provided. Write clearly and legibly. Answer each multiple choice question by marking the space provided. The calculation of grades from the multiple choice questions will deal with the observation that random choices will give a number of correct answers. Please do not write in the space below. Question Points Score General 50 Patterns 30 Observer 26 Total: 106

2 MSO Exam, Page 1 of 7 November 7, 2016 Question 1: General (50 points) For questions (a) to (m), give one answer. (a) (3 points) Which of the following statements is false? Use cases document the functional requirements of a software system. A fully-dressed use case documents the main success scenario, together with alternative exceptional scenarios. Use cases help determine complex design decisions as early as possible. Use cases are read by both developers and end users. (b) (3 points) Which of the following statements does not belong to the three basic principles for object oriented design patterns. Design to an interface, not to an implementation. Distinguish Model, View and Controller classes. Favour aggregation over inheritance. Find what varies and encapsulate it. (c) (3 points) Which of the following statements is false: Refactoring should never change the interface of a class or component. Refactoring aims to make code easier to maintain and extend; Before applying a refactoring to a section of code, a set of automatic unit tests is highly desirable. Refactoring is best done in small steps; (d) (3 points) Which of the following statements is false: Failing to satisfy a method s precondition is the fault of the class calling that method. A method may return a result satisfying a stronger postcondition than the one specified by its contract. Pre- and postconditions can be automatically inferred from a casual use case. Design by contract can be applied throughout the entire process of analysis and design. (e) (3 points) Which of the following statements is false: The Singleton pattern limits the number of instances of a certain class; The Object Pool pattern restricts access to the instances of a certain class; The Singleton pattern and Object Pool pattern are creational patterns; All creational patterns restrict how classes can be instantiated. (f) (3 points) Which of the following statements is true: The Bridge pattern is an instance of the Strategy pattern; The Bridge pattern makes it easier to add new implementations, provided they support the correct interface. The Bridge pattern is best used to decouple the Model from the View, when applying the MVC pattern; Adapting the interface defined by the Bridge pattern requires few changes to existing classes.

3 MSO Exam, Page 2 of 7 November 7, 2016 (g) (3 points) Which statement about the Strategy and Bridge patterns is true? The UML diagrams of these patterns are very similar. The UML diagrams of these patterns are very different. The variants on the right side in the diagram of the Bridge pattern will generally give different results. The variants on the right side in the diagram of the Strategy pattern will generally give identical results. (h) (3 points) Which one of the following statements is false? Unit tests test a single unit of code. This could be a method, class or interface. In test-driven development programmers to start by writing tests, even if these fail. Software testing is the automatic checking whether a piece of software satisfies all its requirements. A good test suite tests both the main success stories associated with a system s behaviour and the exceptional error cases. (i) (3 points) Which one of the following statements is false? In your domain model, you should favour associations over referring to other conceptual classes using a key or identifier. The domain model should focus on modelling the real world, rather than software systems. The domain model should be specified using the Unified Modelling Language (UML). Performing a noun-verb analysis can help identify conceptual classes in your domain. (j) (3 points) What is the intent of the Strategy pattern? To match an existing object beyond your control to a particular interface. To simplify how an existing system is used by defining your own interface. To define the skeleton of an algorithm, deferring some steps to subclasses. To use different algorithms depending on the context in which they occur. (k) (3 points) What happens when you break the Liskov Substitution Principle? This may result in unexpected behaviour when using instances of the subclasses involved. You cannot use polymorphism to use a subclass when a method expects an argument of its parent class. The information encapsulated by an abstract class may become visible to the class s clients. You fail to program to an interface, instead of an implementation. (l) (3 points) Why is software architecture important? Give the answer that is false. Applications become more complicated and use different technologies. Quality assessment cannot be done at the level of code. Software architecture provides you with a vocabulary to discuss your design decisions. Thinking about software architecture is absolutely essential for good performance. (m) (3 points) Which approach to software architecture failed due to complexity? CORBA XML Web services Enterprise Java Beans

4 MSO Exam, Page 3 of 7 November 7, 2016 (n) (11 points) Which of the following statements holds of the UML diagram below? You will receive one point for each correct answer; one point deducted for each wrong answer. ClassA # attributea + attributeb - attributec + methoda() # methodb() ClassD # methoda() + methodb() ClassB + methodc() ClassC - methodd() ClassA is abstract ClassB is a subclass of ClassA ClassD depends on ClassC When implementing methoda in ClassD, you can refer to attributeb. When implementing methodb in ClassD, you can refer to attributec. When implementing methodd, you can refer to attributec When implementing methodc, you can refer to attributea. When implementing methodb in ClassD, you can refer to methoda in ClassD When implementing methodc, you can refer to methodd When you have an object of type ClassC, there is nothing you can do with it because it has no public methods or attributes. Question 2: Patterns (30 points) You have been asked to design a new version of PizzaMaker Deluxe, the latest version of a software package to automate the production of a variety of pizzas. PizzaMaker Deluxe can produce different kinds of pizzas. Besides regular pizzas, PizzaMaker Deluxe can also produce pan pizzas and thin-crust Italian pizzas. Aside from the base, PizzaMaker Deluxe can also add a variety of toppings to a pizza, such as pepperoni, cheese, rucola, or anchovies. For the purpose of this exercise, we will focus on calculating the price of different kinds of pizzas.

5 MSO Exam, Page 4 of 7 November 7, 2016 Pizza Topping Anchovies Pepperoni None Regular Italian Pan Your fellow designer Andrea presents the design(fragment) above. (a) (6 points) Which pattern do you recognize? Adapter Template Strategy Decorator (b) (6 points) Which pattern would you prefer for this case? Adapter Template Strategy Decorator (c) (10 points) Redraw the diagram above according to your preferred pattern. State clearly which classes are abstract.

6 MSO Exam, Page 5 of 7 November 7, 2016 Now suppose that we need to calculate the price of a custom-made pizza. Here is a fragment of the price calculation: regular pizza (without toppings) 5.00 pan pizza (without toppings) 6.00 italian pizza (without toppings) 6.00 pepperoni 1.00 extra anchovies 1.00 extra cheese 0.50 extra For the price calculation, we add the following method to the class Regular. public float price () { return 5.00; } (d) (8 points) Write two more code fragments for the body of price(), one for the class Italian and one for the class Anchovies. There are only two kinds of bodies possible: { return...; } or { return ; }

7 MSO Exam, Page 6 of 7 November 7, 2016 Question 3: Observer (26 points) Have a look of the abstract interface part of the Observer pattern. We have the following structure for simulating a situation where football supporters are in the same room. There are two classes: AjaxSupporter and FeyenoordSupporter, abbreviated as AS and FS. The state of a supporter can be silent or singing. We focus on the situation where one Ajax-supporter and one Feyenoord-supporter are in the same room. When a supporter is silent, he can start singing at any moment, based on a, rather low, random value. When a F-supporter hears an A-supporter singing, the probability that he starts singing increases. When the A-supporter stops singing, the probability that the F-supporter starts singing decreases. When a supporter starts singing, he will be silent again after a certain amount of time. The abstract class Supporter, superclass of AS and FS, has the following methods. public void setsingingprobabilityhigh (); public void setsingingprobabilitylow (); public bool getstate(); // true means singing, false means silent (a) (12 points) Make the class diagram complete.

8 MSO Exam, Page 7 of 7 November 7, 2016 (b) (8 points) Write code for the method notify(). You may refer to the observed object by using identifier obob. (c) (6 points) (BONUS) Suppose we extend the situation in a symmetric way. The A-supporter observes the F-supporter and vice versa. Give the class diagram for this situation.