Assignment 4: Abstraction; Constructors

Goals: Learn to use custom constructors, determine structural equality.

Instructions

Make sure you follow the style guidelines that Bottlenose enforces. For now the most important ones are: using spaces instead of tabs, indenting by 2 characters, following the naming conventions (data type names start with a capital letter, names of fields and methods start with a lower case letter), and having spaces before curly braces.

You will submit this assignment by the deadline using the Bottlenose submission system. You may submit as many times as you wish. Be aware of the fact that close to the deadline the Bottlenose system may slow down to handle many submissions - so try to finish early.

There will be a separate submission for each problem - it makes it easier to grade each problem, and to provide you with the feedback for each problem you work on.

The submissions will be organized as follows:

Due Date: Thursday, February 9th, 9:00pm

Practice Problems

Work out these problems on your own. Save them in an electronic portfolio, so you can show them to your instructor, review them before the exam, use them as a reference when working on the homework assignments.

• Problems 18.1 - 18.4 on page 225

• Problem 18.5 on page 229

• Problem 18.6 on page 234

• Problem 19.4 on page 263

Problem 1: Abstracting over Data Definitions

In this problem, our data will represent different kinds of media. Each piece of media has a title and list of available languages for captions. Different kinds of media can also contain additional information as shown in the supplied Media.java file.

Note: none of these methods are properly implemented. As given in the file, they are all stubs that currently return a dummy value, so the code will compile but not yet work.

Warmup: Download the file and work out the following problems:

• Make at least two examples of data for each of the three classes.

• Design the isReallyOld method for each class. TV and YouTube are fairly modern formats, but movies that came out before 1930 are considered really old.

• Design the method isCaptionAvailable for each class, which determines if a given language is available for captions.

• Design the method format which produces a String showing the proper way to display the piece of media in text. Movies are formatted by the title followed by the year in parentheses, such as "The Favourite (2018)". TV episodes are formatted by the show’s title followed by the season and episode number, separated by a period, followed by a dash and then the episode title, such as "Mad Men 1.1 - Smoke Gets In Your Eyes". YouTube videos are formatted by the video’s title followed by the word by followed by the channel name, such as "Threw It On The Ground by thelonelyisland".

Once you have finished these methods and are confident that they work properly, save the work you have done to a separate file. Do not submit the code as written so far. The problems below are the main point of this exercise, and it will be helpful for you to preserve the code written so far as a reference against which to compare your revised code below. Again, submit only the work below.

• Look at the code and identify all places where the code repeats — the opportunity for abstraction.

  Lift the common fields to an abstract class AMedia, which should implement IMedia.

  Make sure you include a constructor in the abstract class, and change the constructors in the derived classes accordingly. Run the program and make sure all test cases work as before.

• For each method that is defined in all three classes decide to which category it belongs:

  • The method bodies in the different classes are all different, and so the method has to be declared as abstract in the abstract class.

  • The method bodies are the same in all classes and it can be implemented concretely in the abstract class.

  • The method bodies are the same for two of the classes, but are different in one class — therefore we can define the common body in the abstract class and override it in only one derived class.

  Now, lift the methods that can be lifted and run all tests again.

Submit your work in a file named Media.java.

Problem 2: Working with Custom Constructors, A Taste of Equality

A BagelRecipe can be represented as the amount of flour, water, yeast, salt, and malt in the recipe. A perfect bagel results when the ratios of the weights are right:

• the weight of the flour should be equal to the weight of the water

• the weight of the yeast should be equal the weight of the malt

• the weight of the salt + yeast should be 1/20th the weight of the flour

Design the BagelRecipe class. The fields should be of type double and represent the weight of the ingredients as ounces. Provide three constructors for this class:

• Your main constructor should take in all of the fields and enforce all above constraints to ensure a perfect bagel recipe.

• Provide another constructor that only requires the weights of flour and yeast, and produces a perfect bagel recipe.

• Provide another constructor that takes in the flour, yeast and salt as volumes rather than weights, and tries to produce a perfect recipe. Here, too, a perfect recipe should be enforced.

Flour and water volumes are measured in cups, while yeast, salt, and malt volumes are measured in teaspoons.

You should use an IllegalArgumentException with a helpful message if the above constraints cannot be enforced.

Submit your work in a file named Bagel.java.