CSE 142 Homework 2

April 15, 2003

 

Purpose: This homework has three parts, with the following goals.

·        The goal of the first part is to practice your modeling and design skills.

·        The second and third part should improve your programming skills, including loops.

 

Turn-in and due date: The due date is Tuesday April 22 at 9 pm for electronic turn-ins, and Wednesday April 23 in lecture for paper copy turn-in. More below.

 

Time: Parts 1 and 2 should take 1-2 hours. Part 3 will likely take several hours. Make sure you manage your time efficiently.

1 – Modeling

 

Purpose: To practice your modeling skills.

 

Procedure: You need to create a high-level design for a mobile phone. In the earlier media player assignment you were free to express your design any way you wanted to. However, this time you should closely follow the format of the sample media player design provided as a solution to homework 1.

 

Turn-in: Please turn in a single document using the web turn-in form.  The due date is Tuesday April 22 at 9 pm. The best way to ensure that your TA can read your document is to use a recent version of word, or a plain text editor.

 

Hints:

• Quality is much more important than quantity. Be brief, yet concise.
• Don’t spend more than 1-2 hours on this; it is not intended to be tricky, just as an exercise in thinking about what classes and objects a program might contain, and their properties, responsibilities and interactions.
• The design part of homework 1 was very hard because it was so open-ended. Those of you who put effort into it have learned a lot about how difficult it is to express a design well. This time your creativity in expressing the design is very limited – you have to follow our rules. Instead you get a chance to concentrate on creating the design.
• When grading, the TAs will take into account how well the format of your solution conforms to the sample media player design.

2 – Calculator Extensions

 

Purpose: Practicing your programming skills and introducing loops.

 

Procedure: Using either your own calculator or the sample solution code for homework 1 (Calculator.java, CalculatorTestHarness.java), add the following functionality:

• A function square to compute the square of a number.
• A function cube to compute the cube of a number.
• A function inverse to compute the inverse of a number – given an integer n, compute 1/n.
• A function pi that returns the constant p.
• A function exp to compute the exponential function over the integer domain – given an integer n, compute eⁿ.
• A function factorial that computes the factorial of a number – given an integer n, compute n! = 1×2×3× ××× ×n. The factorial of a negative number is not defined. The factorial of 0 is 0! = 1.
• A function power to compute the n-th power of a number – given a integer n and a power m, compute n^m.

You also need to modify the test harness provided with homework 1 to test the new calculator functionality.

 

Turn-in: Turn in the new versions of Calculator.java and CalculatorTestHarness.java using the web form, before 9 pm Tuesday April 22. Also hand in the Turin-in Receipt at the beginning of lecture Wednesday April 23.

 

Hints:

• You need to use conditionals in the right places, to deal with negative, zero or positive parameter values.
• You need to use loops in two places.
• You may have discovered that Java has a Math library.   You may not use that library for this assignment.

3 – The Paper Street Soap Company

 

Purpose: Practice using the code constructs you have learned about so far, particularly conditional statements.

 

Problem: The Paper Street Soap Company sells handmade bars of soap, which are distributed in sheets of recycled paper.

• Both the soap and the sheets of paper are of unpredictable sizes.
• The soap-wrapping machine takes an unwrapped bar of finished soap, and the first available piece of paper, and determines if the bar can be wrapped with that paper. 
• If so, the paper is cut into two parts, one of them just large enough for wrapping the bar; the wrapping is done, the bar is marked "wrapped", and the left-over paper is available to try with another bar.

Your eventual assignment is to write the software that controls the operation of the soap-wrapping machine.   Only a part of the code is due on April 22.  The remainder will be due the following week, as a part of Homework 3.

 

Turn-in: Turn in Paper.java, Soap.java and SoapPaperHarness.java using the web turn-in form, before 9 pm Tuesday April 22. Also turn in the Receipt at the beginning of lecture Wednesday April 23. 

 

More Information:

• The eventual solutions will have three classes Soap, Paper, and Wrapper, plus test harnesses.
• The soap class has three properties corresponding to the three dimensions of a bar of soap, and a fourth property recording its wrapped/non-wrapped status.
• The paper class only has two properties corresponding to the two dimensions.
• The paper class is also responsible for cutting a paper object by changing the dimension properties and accounting for the remainder.
• The wrapper class has one responsibility, which is to take a bar of soap and a sheet of paper and attempt to wrap.
• The wrapper is not supposed to work like an assembly line! It only takes one bar of soap and one sheet of paper, attempts to wrap, and then completes. To wrap another bar the wrapping method needs to be invoked again.
• Much conditional fun here.

For the First Week's Assignment:

• Download the starter classes for Paper.java and Soap.java.  They contain much information in the form of comments.  Implement the constructors and the "getter" methods.  Download Wrapper.java and study it, but don't implement yet.
• Write a PaperSoapHarness.java class, which is designed to test thoroughly the methods of Paper.java and Soap.java.   The method of this class should be called main and have exactly the same signature as the main of CalculatorTestHarness.java.  A basic test consists of creating an object (Paper or Soap), then verifying that its dimensions are correct.  For example, if you create a piece of paper with new Paper(10.0, 14.0), then your test method should verify that the length of the new piece of paper is 14.0 and the width is 10.0.  Do this for all dimensions of the objects, for all combinations of sizes from .5 inch to 20 inches, [added 4/18] in increments of 1/4" (see Message Board posting under "Testharness for Paper and Soap".  The test should operate silently unless an error is found; in that case, it should describe the error situation precisely, then continue with the next test.  Perform all of the Paper tests before performing any of the Soap tests.  At the end of all the Paper tests, print a line stating how many tests succeeded and how many failed.  Do the same for the Soap tests.

Hints:

• The Soap and Paper classes you write for the first week can be continued and expanded for the second week.  The testing needed for the second week will be different (details later).
• Start by printing off the starter classes, reading them top to bottom, and sketching some code away from the computer. 
• Don't begin working on the Wrapper class until you have the first week's assignment complete.  You won't be able to turn in Wrapper the first week anyway.
• If there are things you don't understand about the problem itself, figure them out before wasting time writing code that you might have to rewrite anyway.
• If at first you don't see how to write loops to do all the required tests -- forget about the loops (temporarily).  Write code that tests one piece of paper and/or one bar of soap.  Then worry about the loops.