©2010 Felleisen, Proulx, et. al.

4  Understanding Complex Data

Portfolio Problems

Problems:

1. Problem 15.8 on page 175

2. This problem continues the work on mobiles we have started during the lab.

   Design the method draw() that consumes a Canvas and a Posn that represents the point where the top of the mobile will hang. The method draws the mobile with black lines for the struts, and for the hanging lines. For a simple mobile, there should be a disk of the appropriate color and with the size proportionate to its weight shown at the end of the line.

3. This problem continues the work on lists of Strings that you have done on Assignment 3. Design the following methods — use a helper method with accumulator and make sure the purpose statement explains the meaning of the accumulator:

   1. // combine all Strings in this list into one
      String combine();
      

   2. // find the length of the longest word in this list
      int maxLength();
      

      For the second method you will need to know that the class String defines the method

      // compute the length of this String
      int length();
      

   3. Design the method shortWords that produces a list of all Strings that are shorter than the given number.

   4. Design the method startingWith that produces a list of all words that start with the given letter. Provide the starting letter as a String of length one — for example "c" or "Z".

      Java String class defines the following method:

      // does this String starts with the given String
      boolean startsWith(String s)
      

Pair Programming Assignment

4.1  Problem

For this program use the classes you have defined in the earlier assignments that represent the US cities and states.

1. Design the method totalDistance that computes the distance we have to travel from the first city in the list to the last one, going through all cities in the list in the given order.

2. Extra Credit Design the method willReach that computes the distance to the city with the given name in the given state, following the route specified by this list of cities. (Note: There is Manchester in both MA and NH, there is Burlington in MA and VT, etc.) If the city is not on the specified route, give the distance as -1.

4.2  Problem

Start with the file ExcelCells.java.

For this problem you will use the classes that represent the values in the cells of a spreadsheet. For each cell we record the row and column where the cell is located, and the data stored in that cell. The data can either be a numerical (integer) value or a formula. Each formula can be one of three possible functions: + (representing addition), mn (producing the minimum of the two cells), or * (computing the product) and involves two other cells in the computation.

1. Make an example of the following spreadsheet segment:

       |     A    |     B    |     C    |     D    |     E     |
    ---+----------+----------+----------+----------+-----------+
    1  |    8     |     3    |     4    |     6    |     2     |
    ---+----------+----------+----------+----------+-----------+
    2  | mn A1 E1 | + B1 C1  |          |          | * B2 D1   |
    ---+----------+----------+----------+----------+-----------+
    3  | * A1 A2  | + B2 B1  |          |          | mn A3 D1  |
    ---+----------+----------+----------+----------+----------+
    4  |          | + B3 B2  |          |          | mn B4 D1  |
    ---+----------+----------+----------+----------+-----------+
    5  |          | + B4 B3  |          |          | * B5 E4   |
    ---+----------+----------+----------+----------+-----------+
     

2. Draw on paper this spreadsheet and fill in the values that should show in each cell.

3. Design the method value that computes the value of this cell.

4. Design the method countFun that computes the number of function applications needed to compute the value of this cell.

5. Design the method countPlus that computes the number of Plus applications needed to compute the value of this cell.

   Make sure you design templates, use helper methods, and follow the containment and inheritance arrows in the diagram.

4.3  Problem

Revise the solution to the problem from last week that dealt with bank accounts.

1. Define an abstract class AAccount and lift into it all fields that are common to all accounts.

2. Revise the method amtAvailable for the classes that represent bank accounts: can it be lifted to the abstract class? - or does it have to be defined in each class anyway?

3. Revise the method moreAvailable that determines whether one account has more available for withdrawal than another account: can it be lifted to the abstract class? - or does it have to be defined in each class anyway?

4. Revise the method withdraw that produces a new account with the given amount withdrawn: can it be lifted to the abstract class? - or does it have to be defined in each class anyway?

   Note: Later we will learn how we can signal that the transaction is not valid.

5. Define the method sameName that determines whether two accounts have the same name.

4.4  Problem

Make a final revision of your game. Where appropriate, add lists of game components, or other collection of objects.

The grading rubric for this problem will be as follows:

• 4 points — well designed and readable data definitions and code

• 4 points — examples of world at the start, at the end, and during the game

• 4 points — well designed methods, the design follows one task - one method rule, the methods are defined in the appropriate classes

• 4 points — tests for all methods