Assignment 3     ©2011 Felleisen, Proulx, Chadwick, et. al.

Designing Methods for Simple Classes


Due: 2/1/2011

Portfolio Problems

Work out the following exercises from the textbook as complete programs. You do not need to work out all the methods, but make sure you really understand the design process.


  1. Problem 10.3 on page 97

  2. Problem 10.4 on page 97

  3. Problem 11.2 on page 116

  4. Problem 12.1 on page 129

  5. Problem 12.4 on page 131

Pair Programming Assignment

Read through the JavaWorld tutorial, accessible from the Assignment main page, or at:

Download the new JARS (FunJava-2.jar and JavaWorld-2.jar) and add them to your project’s build-path for this assignment. Try out some of the example programs and review the documentation. You don’t need to submit the examples, we’ll be using Images and World.display(...) later in this assignment.

3.1  Problem

Start with your file from Problem 2.1 in the previous assignment. In your Trac/SVN directory Assignment-03 save these problems (again) in

  1. Adjust your data definitions so that you can represent the cities given in the capitals.txt file.

    In Java you cannot represent zip-codes, such as 02115, as numbers (int or double) for two reasons. First, with the leading zero removed the number is displayed as 2115. Second, and more importantly, numbers that start with the character 0 are considered to be in octal notation (base-8). The zip code 02115 when translated from base-8 to base-10 becomes:

    (2 * 512) + (1 * 64) + (1 * 8) + 5 = 1101

    To avoid these issues, represent zip-codes as Strings, (e.g., "02115").

Design the following methods for your class that represents a City:

  1. the method isSouthOf that determines whether this City is located South of a given City.

  2. the method distanceTo that computes the distance in miles from this City to a given City. (See the problem 1.1, D for help with computing the distance.)

  3. the method, toPosn, that produces a Posn that corresponds to the location of this City in a Scene. Add:

         import image.*;

         import world.*;

    statements to the beginning of your file to use the Scene and Posn classes from the JavaWorld library.

    The Scene class contains methods called width() and height(), which can be used to scale the location. Posn is a simple class with x and y integer fields, that can be constructed with an expression like:

         new Posn(5, 7)

  4. the method place that adds this City (as a small Circle or Star) to a given Scene at the correct location (translated latitude and longitude). You may also want to add the name of the City using a Text image.

    You can test your method(s) using World.display(...) in a testDisplay (or similarly named) test method in your Examples class.

Complete the design of the following interfaces, classes, and methods:

  1. Define the interface and classes needed to represent a list of cities. Our convention is to name these ILoCity, MtLoCity, and ConsLoCity.

    Make examples of at least three lists: the empty-list, a list with a single city, and one with at least three cities.

3.2  Problem

The file contains the definitions of classes the represent bank accounts. In your Trac/SVN directory Assignment-03 add to the file and save these problems in

  1. Make examples of the following accounts:

    • A checking account for Adam Smith with an ID of 123, a current balance of $150, and a minimum balance of $50.

    • A savings account for Betty Jones with an ID 456, a balance of $120, and interest rate of 2.5%.

    • A certificate of deposit account for Pat Malloy with an ID of 789 and a balance of $300 that has not yet matured.

  2. Design the method amtAvailable for these interface and classes that produces the amount the customer can currently withdraw from this IAccount.

  3. Design the method moreAvailable that determines whether this IAccount has more available for withdrawal than a given IAccount.

  4. Design the method withdraw that produces a new IAccount with the balance reduced by the given amount. If the given amount exceeds the available amount, then no money should be withdrawn (i.e., return this).

    Note: Later we will (graduate, and) learn how to signal that the transaction is invalid.

3.3  Problem

The file contains the data definitions, examples of data, and the method countWeights. Review the file, and in your Trac/SVN directory Assignment-03 add to this file and save your problems in

Make sure you keep updating the Templates as you go along. (We have already started you on your way.)

  1. Make an additional Mobile example that represents the following Mobile. The number of dashes in the struts and lines represents their length:

              - - - - - - - - - - - -
             |                       |
            15                       |
           blue           - - - - - - - - - -
                         |                   |
                         |                   |
                         |                  20
                      - - - - - -           red
                     |           |
                    10           |
                   green         |

  2. Design the method totalWeight that computes the total weight of this Mobile. The length and strut (leftside/rightside) weights are given by their lengths (a rightside of 5 adds a weight of 5).

  3. Design the method height that computes the height of this Mobile. Only the lengths contribute to the height of a Mobile, not the struts.

  4. Design the method isBalanced that determines whether or not this Mobile is balanced.

    A Simple Mobile is always balanced. A Complex Mobile is balanced if every sub-mobile is balanced and the weight on the left multiplied by the length of the left strut equals the weight on the right multiplied by the length of the right strut.

  5. Design the method place that places this Mobile into a given Scene. Remember to import image.*; at the top of your file. Hint: You’ll want accumulate the current x and y locations to add sub-mobiles to the Scene in the right spot. Feel free to represent the weight of a Simple Mobile by the size of a Circle or Rectangle. See the documentation for addLine(...) and placeImage(...) in the Scene class.

    Test your method by placing import world.*;at the top of your file and using World.display(...) on one of your Complex examples. Adjust the width/height of the initial EmptyScene, x, and y and scale the lengths/struts to make it look nice.

    Here’s my resulting placement of the example above in a 300 x 180 Scene, starting at (120, 20).

Last modified: Sunday, January 23rd, 2011 8:36:36pm