Deadline

This work should be completed before Friday 2nd October.

Instructions

For instructions on how to do and submit the assignment, please see the assignments section of the course instructions.

Preparation

You must read and answer the questions in the OLI material:

• Read Module 5: Grouping Objects
• If you have not done so, goto https://kth.oli.cmu.edu/, signup and register for the course key dd1337-ht20

You may wish to also read Chapter 4 (4.1 -- 4.11) from, Objects First with Java.

Github Task:

You must complete the following exercises from the course text. Exercise texts are copied here for your convenience and variations in exercise numbering between the 4th, 5th and 6th editions are noted.

Important 1: There are several versions of the MusicOrganizer project that is used in this week's assignment. See the below listing of the excercises for which version to use where. The projects have already been added to your repos under code/music-organizer-vx, please work with them in those folders!

• 4.14 -- 4.16 music-organizer-v1
• 4.24, 4.26 & 4.27 music-organizer-v3
• 4.30 -- 4.33
• 4.43 & 4.45 music-organizer-v5

Also note that music-organizer-v3/v5 in this repository have been slightly modified from the versions found in the BlueJ projects repository

The audio files have been compressed to a glorious 8kbps to save us some space. If they hurt your ears too much, you can find better quality versions here.

Important 2: The MusicOrganizer project makes use of a 3rd party library (javazoom) to help play music. BlueJ will handle the import of these libraries, but if you plan to use another tool, then you have to be prepared to learn a little about the classpath. In short, we need to point the compiler (javac) and runtime (java) to where these extra libraries are stored. For example, to compile on you need extra arguments (-cp the classpath):

# UNIX/Linux/macos
javac -cp +Libs/jl1.0.1.jar:. MusicOrganizer.java

# Windows
javac -cp +Libs/jl1.0.1.jar;. MusicOrganizer.java

Note we need to also include the current directory (:. or ;. on Windows) at the end of path to find MusicOrganizer.class. To run the MusicOrganizer we need to include a main() method and enough code to make it do something:

public static void main(String[] args) {
    MusicOrganizer mo = new MusicOrganizer();
    mo.addFile("audio/BigBillBroonzy-BabyPleaseDontGo1.mp3");
    mo.startPlaying(0);
}

And then launch the runtime, again including the classpath as before:

# UNIX/Linux/macos
java -cp +Libs/jl1.0.1.jar:. MusicOrganizer

# Windows
java -cp +Libs/jl1.0.1.jar;. MusicOrganizer

Please commit any written answers to the docs folder, and commit any Java code developed to the src folder of your KTH Github repo. Remember to push to KTH Github.

Exercise 4.14 (src - use music-organizer-v1)

Add a method called checkIndex to the MusicOrganizer class. It takes a single integer parameter and checks whether it is a valid index for the current state of the collection. To be valid, the parameter must lie in the range 0 to size()–1.

If the parameter is not valid, then it should print an error message saying what the valid range is. If the index is valid, then it prints nothing. Test your method on the object bench with both valid and invalid parameters. Does your method still work when you check an index if the collection is empty?

Exercise 4.15 (src - use music-organizer-v1)

Write an alternative version of checkIndex called validIndex. It takes an integer parameter and returns a boolean result. It does not print anything, but returns true if the parameter’s value is a valid index for the current state of the collection and false otherwise. Test your method on the object bench with both valid and invalid parameters. Test the empty case too.

Exercise 4.16 (src - use music-organizer-v1)

Rewrite both the listFile and removeFile methods in MusicOrganizer so that they use your validIndex method to check their parameter, instead of the current boolean expression. They should only call get or remove on the ArrayList if validIndex returns true.

Exercise 4.24 (src - use music-organizer-v3)

The for-each loop does not use an explicit integer variable to access successive elements of the list. Thus, if we want to include the index of each file name in the listing, then we would have to declare our own local integer variable (position, say) so that we can write in the body of the loop something like:

System.out.println(position + ": " + filename);

See if you can complete a version of listAllFiles to do this. Hint: You will need a local variable declaration of position in the method, as well as a statement to update its value by one inside the for-each loop. One of the things this exercise illustrates is that the for-each loop is not really intended to be used with a separate index variable.

Exercise 4.26 (src - use music-organizer-v3)

In listMatching, can you find a way to print a message, once the for-each loop has finished, if no file names matched the search string? Hint: Use a boolean local variable.

Exercise 4.27 (src - use music-organizer-v3)

Write a method in your version of the project that plays samples of all the tracks by a particular artist, one after the other. The listMatching method illustrates the basic structure you need for this method. Make sure that you choose an artist with more than one file. Use the playAndWait method of the MusicPlayer, rather than the startPlaying method; otherwise, you will end up playing all the matching tracks at the same time. The playAndWait method plays the beginning of a track (about 15 seconds) and then returns.

Exercise 4.30 (src)

Assistant's requirement: Exercises 4.30-4.33 should be submitted in a class called Loops in a file called Loops.java.

Write a while loop (for example, in a method called multiplesOfFive) that prints out all multiples of 5 between 10 and 95.

Assistant's requirement: The method must be called multiplesOfFive.

Exercise 4.31 (src)

Write a while loop to sum the values 1 to 10 and print the sum once the loop has finished.

Assistant's requirement: The method should be called printSum.

Exercise 4.32 (src)

Write a method called sum with a while loop that adds up all numbers between two numbers a and b. The values for a and b can be passed to the sum method as parameters.

Assistant's requirement: The method signature should be sum(int, int), and the result should be returned.

Exercise 4.33 (src)

Write a method isPrime(int n) that returns true if the parameter n is a prime number, and false if it is not. To implement the method, you can write a while loop that divides n by all numbers between 2 and (n–1) and tests whether the division yields a whole number. You can write this test by using the modulo operator (%) to check whether the integer division leaves a remainder of 0 (see the discussion of the modulo operator in Section 3.8.3).

Exercise 4.43 (src - use music-organizer-v5)

The following exercises present a challenge because they involve using some things that we have not covered explicitly. Nevertheless, you should be able to make a reasonable attempt at them if you have a comfortable grasp of the material covered so far. They involve adding something that most music players have: a “shuffle,” or “random-play,” feature.

The java.util package contains the Random class whose nextInt method will generate a positive random integer within a limited range. Write a method in the MusicOrganizer class to select a single random track from its list and play it.

Hint: You will need to import Random and create a Random object, either directly in the new method or in the constructor and stored in a field. You will need to find the API documentation for the Random class and check its methods to choose the correct version of nextInt. Alternatively, we cover the Random class in the next chapter.

Exercise 4.45 (src - use music-organizer-v5)

Write a method to play every track in the track list exactly once in random order.

Hint: One way to do this would be to make a copy of the list and then repeatedly choose a random track from the list, play it, and remove it from the list until the list is empty.

Assistant's note Remember that simply assigning a reference of a List is not the same as copying. The easiest way to actually copy a list is to use a copy constructor.

// assume that we a have string list called someList
// then, this is NOT how to copy it
List<String> thisIsNotACopy = someList;

// But this will
List<String> thisIsACopy = new ArrayList<String>(someList);

Grading Criteria

Each week we will communicate grading criteria through the issue tracker. Grading criteria set the basic standards for a pass, komp or fail, so it is essential you review them each week. These will change over time as your skills develop, so make sure you read the grading criteria issue carefully and tick off all the requirements.