CS 122/132 Midterm Exam Winter 2003

Transcription

1 Date: 24-Feb-2003 Time: 7:00 pm - 9:00 pm Permitted Aids: None CS 122/132 Midterm Exam Winter 2003 Printed Last Initials: ID: Signature: Please check off your PRActicum section from the list below: Arnie Dyck Steven Furino Mark Giesbrecht Jack Rehder 10:30 10:30 unsure 12:30 2:30 unsure 12:30 2:30 unsure 8:30 8:30 unsure Instructions: (Read carefully before the exam begins): 1. Before the exam begins, make certain that you have 9 pages in this booklet and 1 context sheet (double sided). 2. Before the exam begins, fill in information about yourself on this page. 3. The yellow paper contains a case study which forms the basis for almost every question in the exam. When the exam begins, turn the yellow page over and read it carefully. 4. Answer all questions in this booklet. If additional space is required, use page 9. Label work clearly, both on page 9 and where the question is asked. 5. Additional paper is available upon request. 6. The marks assigned to each question are shown at the beginning of the question. Use this information to organize your time effectively. There are a total of 100 marks available. 7. Some multiple choice questions ask you to circle all of the correct answers. These questions have a penalty for wrong answers. Other multiple choice questions ask you to circle one answer. These questions do not have a penalty for wrong answers. 8. Questions will not be interpreted. Proctors will confirm or deny errors in the questions only. If you consider the wording of a question to be ambiguous, state your assumptions clearly and proceed to answer the question to the best of your ability. Your assumptions may not trivialize the question. 9. Documentation is always appreciated, but is not required unless explicitly requested. 10. Cheating is an academic offense. Your signature on this exam indicates that you understand and agree to the University s policies regarding cheating on exams. Marks: 1-5. / / 8 7. / / / / 14 / 100 Page 1 of 9

2 1. [3] The printcompany method in the YellowPages class has a single parameter cname containing a company name. Circle all of the following that could be used to print the number of categories under which that company is listed in the Yellow Pages. a) Company c = this.clist.findcompany(cname); System.out.println(c.categories.size()); b) System.out.println(this.clist.length); c) System.out.println(this.clist.findCompany(cName).listCategories().length); d) System.out.println(this.listCategories().length); e) None of a, b, c, or d. 2. [4] A category is undersized if it has only one company in it and that company has advertisement level 0 or advertisement level 1. Assume that catname is a String containing a valid category name, and the following line of code has just been executed: Company[] cl = clist.companiesin(catname); Each of the following boolean expressions is in a method in the CompanyList class. Circle all of the boolean expressions that return true if the category named by catname is undersized. a) cl.length==1 && (this.getrevenue()==yellowpages.adcosts[0] this.getrevenue()==yellowpages.adcosts[1]) b) cl.length==1 && (cl[0].getrevenue()==yellowpages.adcosts[0] cl[0].getrevenue()==yellowpages.adcosts[1]) c) cl.length<2 && cl.getrevenue()==yellowpages.adcosts[0] d) ( cl.length==1 && cl[0].getrevenue()==yellowpages.adcosts[0] ) ( cl.length==1 && cl[0].getrevenue()==yellowpages.adcosts[1] ) e) cl.length==1 && cl[0].getrevenue()==yellowpages.adcosts[0] && cl[0].getrevenue()==yellowpages.adcosts[1] 3. [3] Which of the following methods in the class Company could be made static (you may circle more than one answer)? a) A method compare which takes two company objects as parameters, and returns a boolean. It returns true if the two objects are equal and false otherwise. b) A method equals, which takes a single company object as a parameter, and returns a boolean. It returns true if the object this is equal to the object in the parameter, and false otherwise. c) A method addtocategory, which takes a String specifying a category as a parameter. The category is added to the list of categories to which the company belongs. d) A method getcompanyid which returns a unique integer ID for the company. Assume there is a static instance variable nextid in the class Company which is incremented by the constructor whenever a new company object is created. The ID is set to this counter on construction. e) A method totalcompaniescreated, which returns the total number of times a company object has been created. Assume there is a static instance variable nextid in the class Company which is incremented in the constructor whenever a new company object is created. Page 2 of 9

3 4. [4] Consider the following code, which uses the partially filled array companies in the CompanyList class. int count=0; for (int i=0; i <= companies.length; i++) { if (this.companies[i].incategory( Musical Recordings )) { count++; Which two exceptions could this code throw and under what conditions? a) b) 5. [4] A method signature is the first line of the method. It includes the visibility modifier (e.g., public), the return type, the name of the method and the parameters. Write signatures for new methods in the CompanyList class which address the following use cases: a) Finds the companies whose names begin with a specified character: b) Finds the number of companies which belong to a specified list of categories: 6. [8] The method listcategories() in the Company class returns an array of String objects containing the categories under which the company is listed (and only these strings it is not partially filled). Provide the complete code for the listcategories method. Note that the instance variable categories is an ArrayList, not an array. Page 3 of 9

4 7. [20] This question has two parts that involve computing the revenue generated for the Yellow Pages. a) [5] Implement the getrevenue method in the Company class. This method returns the total dollars paid by the company to be listed in the Yellow Pages. The revenue is calculated by multiplying the number of categories in which the company is listed times the cost for the company s advertisement level. This cost for the company s advertisement level is found by looking in the YellowPages.ADCOSTS array of constants in the YellowPages class. For example, in the example in Figure 1 of the context, for the company Future Shop, the getrevenue method will return 900. b) [15] Implement the maxrevenue method in the CompanyList class. This method returns a company object which belongs to the category cat whose revenue is at least as large as the revenue of any other company belonging to the category cat. In other words, its revenue is the maximum of all companies in category cat. Revenue for a company is calculated using the getrevenue(). Recall that companies is stored as a partially filled array. public class CompanyList extends Object { public Company maxrevenue(string cat) { Page 4 of 9

5 8. [24] Using the design presented in the UML, implement the YellowPages, CompanyList and Company constructors to read a data file using the format shown in the program specification. You may read the file only once, due to the inefficiency of file operations. a) [4] The YellowPages constructor: b) [12] The CompanyList constructor (write any helper methods at the top of the next page). Page 5 of 9

6 Question 8 continued.. Helper methods for the CompanyList constructor (if appropriate) go here c) [8] The Company constructor Page 6 of 9

7 9. [16] Listed below are four attempts to implement the delcompany method in the CompanyList class. The delcompany method is designed to delete a company from the partially filled array companies in the class CompanyList. The company is specified by a Company object. Each company is assumed to appear at most once in the list, and the order of the companies in companies does not matter. If the specified company is not found, an error is printed. Each attempt contains at least one error. Find the errors in each and fix them in the code. In all cases your changes must be the smallest change that will fix the problem. In all cases at most three changes are needed. public void delcompany(company c) public void delcompany(company c) { for (int i=0; i<this.numcompanies; i++) { if (this.companies[i].equals(c)) { for (int j=i; j<this.numcompanies-1; j++) { int i = 0; while (!this.companies[i].equals(c) ) { i++; { this.companies[i]=this.companies[i+1]; return; if (i==this.companies.length) System.out.println( Error: not found ); { System.out.println( Error: not found ); else { while (i<this.numcompanies-1) { this.companies[i]=this.companies[i+1]; public void delcompany(company c) { int k = 1; for (int i=0; i<this.numcompanies; i++) { if (this.companies[i].equals(c)) { k=i; if (i>=this.numcompanies) { System.out.println( Error: not found ); else { this.companies[k] =this.companies[this.numcompanies-1]; this.numcompanies--; public void delcompany(company c) { boolean found = false; int i=0; while (i<this.numcompanies &&!found) { found = this.companies[i].equals(c); if (!found) { System.out.println( Error: not found ); else { for(int j=i; i<this.numcompanies; i++) { this.companies[j-1]=this.companies[j]; Page 7 of 9

8 10. [14] One improvement that could be made to our design is to write a separate Category class, rather than just using Strings. Each Category object contains the name of the category (a String) and an ArrayList of other similar categories (for example, the Automobile category might list Car and Truck as similar categories). Methods for getting the category name, and for adding to and deleting from the similar categories are provided, along with appropriate constructors. A CategoryList class holds a list of Category objects. Methods for searching for a category object by name, adding and deleting a Category (by position in the list) would be useful. a) [10] Provide a simple UML diagram for the Category and CategoryList classes. Specify instance variables and method signatures for the actions described above. b) [4] If it is necessary to maintain a list of all categories that appear anywhere in Yellow Pages, in which class should this list be stored as an instance variable? Briefly justify your decision. Page 8 of 9

9 Additional Solution Space or Space for Rough Work Page 9 of 9