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Instructions
Practice Problems
Problem 1: Abstracting over Data Definitions
Problem 2: Working with Custom Constructors, A Look at Equality
8.5

Assignment 4: Abstraction; Constructors

Goals: Learn to abstract common code and use custom constructors.

Instructions

Be very, very careful with naming! Again, the solution files expect your submissions to be named a certain way, so that they can define their own Examples class with which to test your code. Therefore, whenever the assignment specifies:
  • the names of classes,

  • the names and types of the fields within classes,

  • the names, types and order of the arguments to the constructor,

  • the names, types and order of arguments to methods, or

  • filenames,

...be sure that your submission uses exactly those names.

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.

This assignment has only one submission date. You will submit each problem separately in handins by the deadline below:

Due Date: Monday, May 19th, 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.

Problem 1: Abstracting over Data Definitions

Related files:
  Beverages.java  

In this problem, our data will represent different kinds of drinks you might order at a coffee shop. Each drink has several attributes, some of which are common to them all and some of which differ.

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:

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.

Submit your work in a file named Beverages.java.

Problem 2: Working with Custom Constructors, A Look at Equality

When dyers create pigment mixes to dye yarn, they combine amounts (in grams) of red, yellow, blue and black pigments. A perfect recipe for a dye mix ensures the relative amounts of the four colors are appropriate:

Design a DyeRecipe class. The fields should be of type double and represent the weight of the four dye colors in grams. A dye recipe is always scaled such that the total amount of dye is 1g. Provide three constructors for this class:

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

Once you’ve completed the above constructors, you should:
  • Remove as much duplicate code as possible from these constructors. (Hint: you may want a Utils class to help with computing or enforcing some of the constraints.)

  • Implement the method sameRecipe(DyeRecipe other) which returns true if the same ingredients have the same weights to within 0.001 grams.

Submit your work in a file named Dyes.java.