Exercise 7:
Design Patterns
Software Engineering Design & Construction
WS 2016/17 - Dr. Michael Eichberg, M.Sc. Matthias Eichholz
Although this exercise is not graded, it is highly recommended to also do them on your own. Just looking at a solution is
much easier in comparison to actually coming up with it. Support can be found in the office hours of our tutors and in
the forum at https://www.fachschaft.informatik.tu-darmstadt.de/forum/viewforum.php?f=234.
Task 1 Scala 2.7 Collections
In the project for the first exercise, you will find the source code for the Scala 2.7 standard library, which contains a
collection hierarchy. Note: do not expect to be able to compile it with a current Scala compiler or in Eclipse / IntelliJ.
We know that Scala 2.7 is an old version, but newer versions are too complex, please do not try to analyze other Scala
versions than 2.7. Analyze how the core of the collections hierarchy makes use of the following design patterns:
• Factory (any variant: abstract factory, factory method)
• Observer
• Strategy
• Template
Look at all of the following classes and traits and their corresponding companion objects:
• Everything in packages scala,scala.collection and scala.collection.mutable that directly or transitively inherits
from scala.Iterable.
• All base traits and base classes of the above traits and classes only if they participate in a pattern.
For each pattern name the participants, which roles they have, how they collaborate and how they might vary from the
standard text book examples. Explain the pattern in terms specific to the current pattern instance, e.g., don’t just copy
text from a design patterns book. Your analysis should be complete and you should mention how often a specific pattern
is used in comparison to others. If a pattern is used in a similar way in many different places, give a detailed analysis of
a single example and say how other instances of the pattern in the collection hierarchy relate to it.
Task 2 Synchronized Maps
Now have a look at the SynchronizedMap trait in the package sc ala. col lect ion .mu tabl e. Which design pattern is used
to add synchronization to maps? Does the design pattern that is used resolve the fragile base class problem? Justify your
answer. For this task you can use the current version of the Scala standard library.
Task 3 Order Management System
The word has spread about your successful implementation of the order management system (OMS) for Starbuzz Inc.
You received an email from the manager of TastyPizza Inc. who heard about your success. He wants you to implement a
new OMS for his pizza delivery shop. For the first milestone, he has defined several requirements that need to be fulfilled
by your OMS:
• The shop offers pizza, several beverages (lemonade, water and wine) as well as some franchise items (shirts,
mugs). The system needs to be able to represent these products.
• All products have a price and pizza and beverages have specific nutrition facts.
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