Many students have been asking what they should focus their study on for each quiz.
This week’s quiz is based on ArrayLists. Having completed and understood all of last week’s lab work you should be able to achieve ‘satisfactory’ on this week’s quiz. You may also want to revise the methods in your first assignment, the ‘Returning to Ticket Machine’ lab and do some practice using arrays and loops.
Here are my solutions to your Week 8 ArrayList and Classes lab. I have added two extension questions. I added comments so that you may follow along with the logic.
I strongly suggest that you try these two questions yourself before checking my solutions. The questions are:
Question 1
Write a method ‘newVIPList’ that takes in an array of strings of VIP member names in the club. The method should take all of the members in the existing club with matching names and return a new array list of members containing only these VIP members.
Question 2
Write a method ‘removeOldMembers’ that takes in a year cut off and removes all the members in the club who joined in a year earlier than the cut off year. This method should not return anything but manipulate the array list field of the club itself.
Please remember these are extension questions that are good practice to test your understanding of ArrayLists and Arrays.
Please Note: I have also included a test method that creates an array of members given a specified size. Feel free to use this and do not worry about the line: String.valueOf(i). It has not been covered in the course thus far and you are not expected to know it.
DOWNLOAD FILES HERE:
Download the BlueJ project club.zip for this week’s exercises. There are three classes in the project that help you to represent a club and its members.
The Member class is fully defined and contains all the methods you need. Note a couple of things we haven’t covered in lectures. The constructor uses a throw statement to create a Java runtime error. Try entering a month with a number outside the range 1 .. 12 and see what happens.
The Member class also defines a method called toString. This returns a string representation of the object. If you try to print the object using System.out.println, the system will used toString to convert your object into a string for printing.
The ClubDemo class is the “main” class that we use to create a club and members and test the other classes.
The Club class is incomplete. The methods in the class are empty and your job is to write the code inside to make them work.
The club class needs a way of storing a collection of members. You should use an ArrayList to do that. The class includes two constructors. Let’s start with the first one. It should initialise the ArrayList and leave it empty.
The Join method is passed a new member as an argument. You should add this member to the ArrayList.
The numberOfMembers should return the number of elements in the ArrayList.
The listMembers method should go through the ArrayList of members and print each one, one per line.
The removeMember method should remove a member from the ArrayList when a member decides to leave the club. The argument to the method is a string, which is the member’s name. You have to search the ArrayList to find the member with that name. Use a simple algorithm, just go through the list, one-by-one until you find the member with the given name and remove it from the ArrayList.
The second constructor in the class allows you to pass an array of members. Initialise the club membership with the members in the array.
NOTE: check this web site regularly for updates and clarifications to the assignment specification.
Due Date: Sunday week 8 (23:59:59 22 September 2013)
ChangeLog:
Suppose you are designing a program for an automated teller machine. The ATM generates transactions that are sent to the banks central computer for processing.
In this assignment, you will create two classes, “Account” and “Transaction”. An Account object should have a unique account number, which can be represented by an integer, and a balance. Initially the balance is zero. A Transaction object should have an amount being transacted and a reference to the Account class associated with the transaction.
Here is an example of the two classes being invoked:
/**
* This class contains a main method that calls methods in the classes you will write.
*
* @author (your name)
* @version (a version number or a date)
*/
public class RunTransactions
{
static void main()
{
// Create two new accounts with the given account numbers
Account fred = new Account(1234);
Account jim = new Account(6778);
// Provide accessor methods for account information.
int accountNumber = fred.getAccountNumber();
float balance = fred.getBalance();
// Transactions consist of an account reference and an amount
Transaction t1 = new Transaction(fred, 20);
Transaction t2 = new Transaction(jim, 10);
Transaction t3 = new Transaction(jim, -20);
// Transactions must contain a "process" method that is called to
// actually perform the transaction.
// A transaction should not be allowed if it results in a negative balance.
t1.process();
t2.process();
t3.process();
// Print out a report of the account balance.
// The format should be like this: Account 6778 has balance $20.0
fred.report();
jim.report();
}
}
Download this file. It contains a BlueJ project with just the RunTransactions class. You must create your own Account and Transaction classes. You can create whatever fields and methods you think appropriate but you must provide methods that can be called exactly as above.
The report method should print out a simple message giving the account number and balance. The format should be
Account <account number> has balance $<account balance>
For example, the output of the reports from the above sample code should be:
Account 1234 has balance $20.0
Account 6778 has balance $10.0
You will learn about main methods and the static qualifier in later lectures. For now, you only need to know that when you right click on the RunTransactions class, you will see an item in the menu void main(). Clicking on this will run the main method, which will call your code.
You may change the main method to test your code with different combinations of accounts and transactions. Only remember that you must use exactly the same names of classes and methods and the types of arguments are return values must be identical.
When you submit your assignment, we test your code with different main methods.
You will submit your assignment to the Give automated marked system.
Checking your submission... Checking for Account.java Account.java Compiled Sucessfully Checking for Transaction.java Transaction.java Compiled Sucessfully Sucessfully compiled against sample RunTransactions.java All files are OK
Submission notes:
The maximum mark for this assignment is 10. Marks will be awarded as follows:
If you’re having trouble with this week’s lab, take a look at the following example and step through the ‘main’ method inside the ‘Main’ class.
A practical exam will be held in the first hour of next weeks lab. You will be given several programming exercises that you will do on the computer and submit using the same give system that you used to submit the first assignment.
The full specification will be given in the lab for next week.
This first task should be attempted before coming to the lab.
Suppose we were writing a program to administer a university. Discuss:
Go back to the ticket machine project you worked on in last week’s tut.
Let’s suppose now that a ticket has 10 charges. Each time we use it, one charge is lost.
Now let’s add a recharge method to the TicketMachine. It should take a Ticket as a parameter and reset its charges to 10 but at the cost of 1/10th of the ticketPrice for every charge added (if the user has enough balance). Implement this in stages:
Take a look at the clock project from Chapter 3 of the textbook.
If you’d like some extra practice writing methods involving loops and arrays, take a look at the following two links:
If you didn’t finish last week’s exercises, continue on with those. In particular, make sure you understand how to use loops and arrays (i.e. the last two exercises).
Investigating the TicketMachine:
Extending the TicketMachine
Let us extend the ticket machine to keep track of the total amount of cash collected and to allow us to change ticket prices.
This assignment is about loops arrays. You will write three methods to manipulate arrays. The first two are easy. The third one will require more thought about the design. You will submit the assignment using the CSE give system (see below).
Download the BlueJ project, Assignment1.zip. It contains three methods. You have to write the code that goes inside them.
The first method finds the average of the elements of an integer array:
public double average(int[] data)
That is, given an integer array, data, calculate what the average of its elements are and return the average value. For example, the average of {1, 3, 2, 5, 8} is 3.8.
The second method is:
public int countInRange(int[] data, int lo, int hi)
For this, you have to count the number of elements of the array, data, that lie in the range lo to hi inclusive, and return the count. For example, if data is the array {1, 3, 2, 5, 8} then the call
countInRange(data, 2, 5)
should return 3 because there are three elements, 3, 2 and 5 that lie in the range 2 .. 5.
The third method, arrayAdd, takes two arrays as parameters and returns a new array that is the sum of the first two.
public int[] arrayAdd(int[] R1, int[] R2)
The addition of two arrays yields an array whose elements are the sum of the corresponding elements in the parameter arrays, i.e.
R1[0] + R2[0], R1[1] + R2[1], R1[2] + R2[2], ....
You will submit your assignment to the Give automated marked system.
================================================ Checking your submission... Checking for Assignment1.java Assignment1.java Compiled Sucessfully All files are OK ================================================
Submission notes: