INFO0062 - Object-Oriented ProgrammingExercise session #5 - Inheritance

Jean-François Grailet

University of Liège

Faculty of Applied Sciences

Academic Year 2017 - 2018

Context

Context Exercises Additional exercise

Sorting your audio library

Media players allow to sort albums in several manners, most notably

• Artist

• Genre

• Year of release

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Today’s program

Re-using your code from the previous session

• We will add new classes to allow album sorting

• We will use inheritance to implement the different policies

• We will also re-organize list classes in the process

If you don’t have a solution to the exercices of the previous session, don’t worry

• You can use the suggested solution1

1available on http://www.run.montefiore.ulg.ac.be/~grailet/INFO0062.php2 / 8

Exercises

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Exercise 1

We want to expand our program from last week to produce two sorted lists of thealbums: one list where the albums are sorted by their respective artist, and anotherlist where the albums are sorted by their year of release (with the earliest works first).Calling toString() on each list should print their content with the details about theartist/year of release when relevant.

Since you already have a list class to build the albums from Audio.db2, and since wewill maintain all lists3, we will have three lists with several similarities.

Your first task is design a superclass AlbumList. Consider these questions:

What are the elements that all lists will have in common ?

How does the existing list class relate to this superclass ?

Should this superclass be instantiable ?

Implement AlbumList and adapt your previous list class in consequence, if necessary.

2to simplify things a bit, additional exercise from previous session is not taken into account.3the point is not to apply sorting algorithms on the first list; see courses like INFO0902 for this specific topic.

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Exercise 2

Our sorted lists will only be created after building the initial list/database. They cantherefore be created by reading the entire initial list to insert each album, one by one.The sorting can therefore occur at the insertion of an album. This consist in visiting thelist being built to see where the new album should be placed to respect the ordering.

Considering the statement above, ask yourself the following questions:

How can you instantiate your ordered lists from the initial database ?

What operations are likely to be identical for building each list ?

Can you translate this into your class hierarchy ?

If yes, how can you use the abstract keyword ?

If necessary, implement the additional class(es) to apply your answers.

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Exercise 3

Using what you implemented during previous exercises, implement the class(es) thatcan produce the sorted lists of albums and update your main() method to display both.Can you still use find() on your new lists ?

Your toString() method(s) should produce the following output (sorting by artist):

- AC/DC -The Razors Edge (1990)Highway To Hell (1979)- Daft Punk -Discovery (2001)Homework (1997)- David Bowie -Blackstar (2016)- Fatboy Slim -Palookaville (2004)Better Living Through Chemistry (1996)...

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Exercise 3 (II)

As for the sorting by year, you should obtain something like this:

- 1976 -Oxygène by Jean Michel Jarre- 1979 -Highway To Hell by AC/DC- 1990 -The Razors Edge by AC/DC- 1996 -Travelling Without Moving by JamiroquaiBetter Living Through Chemistry by Fatboy Slim- 1997 -Oxygène 7-13 by Jean Michel JarreHomework by Daft Punk...

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Additional exercise

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Exercise 4

We implemented a solution to sort our album database by year or by artist. However,albums from a same year or artist are not sorted between themselves; i.e., albumsfrom a same artist could be ordered by year/title, and albums from a same year couldbe sorted by title as well.

Modify your solution such that sequences of albums from a same year or artist are alsosorted by title. Ideally, you should only modify existing child classes of your currentsolution to achieve this goal.

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Exercise 4 (II)

For instance, this is the display you should have for albums sorted by artist:

- AC/DC -Highway To Hell (1979)The Razors Edge (1990)- Daft Punk -Discovery (2001)Homework (1997)- David Bowie -Blackstar (2016)- Fatboy Slim -Better Living Through Chemistry (1996)Palookaville (2004)- Jamiroquai -Automaton (2017)Rock Dust Light Star (2010)Travelling Without Moving (1996)...

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