Assignment 8B SOLUTIONS

Transcription

1 CSIS 10A Assignment 8B SOLUTIONS Read: Chapter 8 Choose and complete any 10 points from the problems below, which are all included in the download file on the website. Use BlueJ to complete the assignment, then export JAR file and upload to the server using your pass code. You may do more than 10 points of work but the max award will be 11 points. Part I: Exam Prep Exercises--7 points total To be answered in the Exercises file Find the Error: in the Exercise file 4. String[] names = "George", "Susan" ; int totallength = 0; for (int i = 0; i < names.length(); i++) xxxxxx it should be: (int i = 0; i < names.length; i++) totallength += names[i].length; xxxxxx it should be: totallength += names[i].length(); 5. String[] words = "Hello", "Goodbye" ; System.out.println(words.toUpperCase()); xxxxx After the word "words" there should be [] with 0 or 1

2 Algorithm Workbench a) String [] scientists = "Einstein","Netwon","Copernicus","Kepler"; b) for (int k=0; k< scientists.length; k++) System.out.println( scientists[k]); c) int total=0; for (int k=0; k< scientists.length; k++) total += scientists[k].length(); System.out.println("total length of all strings in array: " + total); NOT OK. After creating the array of BankAccounts, all cells in the array refer to "null", in other words, there are no actual BankAccounts yet. We have to create a BankAccount object and store a reference to it in cell 0 before we can change the balance or withdraw from it. In other words, INSERT the line acc[0] = new BankAccount( ); right after the first line above. Part 2: Programming Challenges 3 points each 1) Create class P1ChargeValidation and P1ChargeValidationTester and solve the following problem: These numbers are already stored in a file in your Assignment8B download called "accounts.txt". Your ChargeValidation class should store these numbers in a field declared as an array of int.

3 The constructor of your class should load the data from the file into the array. Write an isvalid method. It will use a sequential search to locate the number passed as an argument. If the number is in the array, the method should return true, indicating the number is valid. If the number is not in the array, the method should return false, indicating the number is invalid. Write a program that tests the class by asking the user to enter a charge account number. The program should display a message indicating whether the number is valid or invalid. P1ChargeValidation.java Contains a list of account numbers and a method to check if a given number is in the Andrew import java.util.scanner; //For reading of input! import java.io.; //For opening of files for reading input from! public class P1ChargeValidation //Field for all valid account numbers private int[] validaccounts = new int[18]; Constructor--initializes object with information from accounts.txt public P1ChargeValidation() throws IOException //Open data file File infile = new File("accounts.txt"); Scanner infileinput = new Scanner(inFile); //Read information from file. Will enter in zeroes if it runs out of data from the file. for(int i=0; i<validaccounts.length; i++) if(infileinput.hasnext()) validaccounts[i] = infileinput.nextint(); else validaccounts[i] = 0; infileinput.close(); Sequentially searches the validaccounts field for a test testnum The number to be searched Whether the test number was found in validaccounts. public boolean isvalid(int testnum) boolean searchsuccessful = false; //Search success flag. //Search the array. for(int i=0; i<validaccounts.length && searchsuccessful == false; i++)

4 if(validaccounts[i] == testnum) searchsuccessful = true; //Return result. return searchsuccessful; P1ChargeValidationTester.java Tests the P1ChargeValidation Andrew import java.util.scanner; import java.io.; public class P1ChargeValidationTester public static void main(string[] args) throws IOException P1ChargeValidation accounts = new P1ChargeValidation(); Scanner keyboard = new Scanner(System.in); int testvalue; boolean accountfound; System.out.print('\f'); do System.out.println("Please enter an account number; this program will check if it is valid."); System.out.println("Enter -1 to quit.\n"); testvalue = keyboard.nextint(); accountfound = accounts.isvalid(testvalue); if(accountfound) System.out.println("That account number is valid."); else if(testvalue!= -1) System.out.println("That account number is invalid."); while(testvalue!= -1); 2) Create a new class called P2PhoneBookEntry and P2PhoneBookTest that solves the following problem:

5 The PhoneBookEntry class represents a single person's name The PhoneBookTest class will have a main method that creates the ArrayList<PhoneBookEntry> and adds the PhoneBookEntry objects to the list. P2PhoneBookEntry.java import java.util.arraylist; // Needed for ArrayList class public class P2PhoneBookEntry private String name; private String number; public P2PhoneBookEntry(String phonename, String phonenumber) name=phonename; number=phonenumber; public String tostring() return "name: " + name + ", number: " + number + "\n"; public void setname(string phonename) name=phonename; public void setnumber(string phonenumber) number=phonenumber; public String getname() return name; public String getnumber() return number; P2PhoneBookTest.java import java.util.arraylist; // Needed for ArrayList class import javax.swing.joptionpane; Write a description of class P2PhoneBookTest (your (a version number or a date) public class P2PhoneBookTest

6 public static void main(string[] args) // Create an ArrayList to hold PhoneBookEntry objects. ArrayList <P2PhoneBookEntry> list = new ArrayList<P2PhoneBookEntry>(5); // Add PhoneBookEntry objects to the ArrayList. list.add(new P2PhoneBookEntry("Fred", " ")); list.add(new P2PhoneBookEntry("Josh", " ")); list.add(new P2PhoneBookEntry("Jessica", " ")); list.add(new P2PhoneBookEntry("Marley", " ")); list.add(new P2PhoneBookEntry("Dave", " ")); System.out.print("\f"); // Display each name and number. for (int k = 0; k < list.size(); k++) System.out.println(list.get(k)); // invokes tostring of PhoneBookEntry