Recitation 20 for CS160

Recitation R20 - Classes, Objects, Methods
Fall 2013

CS160: Foundations in Programming

The goal of this lab is:

Write a useful class with no main method
Show how instance data is useful
Instantiate an array of classes
Continue to practice using file I/O

Classes, Objects, Methods

Write the following program from scratch in the following phases:

Phase 1

Create a new project in Eclipse called R20.
Define a new class called Music.java, without a main method.

Define the following as private instance (non-static) data in Music.java:

    private String songTitle;
    private String albumName;
    private String artistName;
    private int releaseYear;

Define a constructor that initializes all variables and methods to get individual variables, as follows:

    // Constructor
    public Music( String title, String album, String artist, int year ) { }

    // Get methods
    public String getTitle() { }
    public String getAlbum() { }
    public String getArtist() { }
    public int getYear() { }

Implement the following method to get the price of the title:
```
    public double getPrice() { }
    
```
The algorithm for determining the price is $1.09 for titles released before 1970, $1.59 for titles released in the 1970's, $0.59 for titles released in the 1980's, $1.19 for titles released in the 1990's, and $1.39 for titles released on 2000 and later. The reasoning for this is that some decades have better music than others!

Phase 2

Create a new class called R20.java, with a main method.
Declare (but do not allocate) an array of Music objects as a class variable (static).
Implement a static method readFile which takes a String parameter with the filename.
Call readFile from your main with args[0] as the parameter.
Here is the data file that you will read for this program: music.txt
Implement readFile as follows:
- Add a scanner to read from the file passed in.
- You will need a try-catch block for this to work.
- If the file cannot be read, print an error message and exit the program.
- Read the number of titles, an integer, from the file.
- Use the number of titles to allocate the array of Music objects.
- Add a for or while loop that reads the remaining lines of the file.
- The format is 4 lines per entry: title, album, artist, year.
Store the data read from the file in the array of Music objects.
NOTE: Even after allocating the array, you must instantiate an individual Music object (by calling the constructor) for each array element. The TA will explain why.
NOTE: After each call to nextInt() you must add a nextLine() call to discard the newline that follows the integer, otherwise the next string you read may be empty. The TA will explain why.

Phase 3

After calling readFile in the main method, iterate the array of Music objects and print out each entry, as follows:

    0: <title 0>, <album 0>, <artist 0>, <year 0>
    1: <title 1>, <album 1>, <artist 1>, <year 1>
    2: <title 2>, <album 2>, <artist 2>, <year 2>
    ...
    n: <title n>, <album n>, <artist n>, <year n>

Make sure that your program correctly reports all titles in the file.
Figure out how much it would cost to buy all titles in the file and print it out:
```
    Total cost: $13.68
    
```

Show your R20.java program to the TA for grading and submit to RamCT to get credit for this lab.

Recitation R20 - Classes, Objects, Methods Fall 2013

Classes, Objects, Methods

Phase 1

Phase 2

Phase 3

Recitation R20 - Classes, Objects, Methods
Fall 2013