# HW 4 Solution

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## Description

This homework has 3 problems. The first problem concerns an ArrayList (Ch 11). The other two problems deal with Ch 13.

Eclipse Reminder

• You will create a Java Project in Eclipse with the name: hw4_FLastname
• You will have three packages: prob1, prob2, prob3.

Problem 1

Do problem 11.13 from the text (p.447). If you need a hint, there is one at the end of this document.

Problem 2

(Use material from Ch. 13) A bank offers two types of accounts to its customer: RegularAccount and PremiumAccount. All accounts have a balance and methods: deposit and withdraw which both accept an amount of money and either adds to the balance (deposit) or subtracts the amount from the balance (withdraw). An account also has a toString method that returns a string like this:

The balance is \$3,603.35.

Accounts also have an applyInterest method that calculates the interest and then adds this to the balance. However, interest is calculated differently for the two types of accounts. A RegularAccount earns 1% interest for the balance over \$1000. The PremiumAccount earns 1.5% interest on the entire balance.

Do the following:

1. Model this situation with a class diagram. You will add to this diagram for Problem 3.

Hint: Design “Account” as an abstract class. You may define its balance as a protected data field

1. Write the required classes.
2. Write a tester, java and use the following main to test:

Account ac1 = new RegularAccount(500);

System.out.println(ac1);

ac1.applyInterest();

System.out.println(ac1);

ac1.deposit(1200);

System.out.println(ac1);

ac1.applyInterest();

System.out.println(ac1);

ac1.withdraw(1000);

System.out.println(ac1);

ac1.applyInterest();

System.out.println(ac1);

1

System.out.println(pacc1);

pacc1.applyInterest();

System.out.println(pacc1);

pacc1.deposit(1200);

System.out.println(pacc1);

pacc1.applyInterest();

System.out.println(pacc1);

The code should output the following:

Regular Account: The balance is \$500.00

Regular Account: The balance is \$500.00

Regular Account: The balance is \$1700.00

Regular Account: The balance is \$1707.00

Regular Account: The balance is \$707.00

Regular Account: The balance is \$707.00

Premium Account: The balance is \$500.00

Premium Account: The balance is \$507.50

Premium Account: The balance is \$1707.50

Premium Account: The balance is \$1733.11

Problem 3 (code + class diagram)

First:

1. Create a prob3 package in Eclipse.
2. Copy these classes: Account, RegularAccount, PremiumAccout from prob2 to prob3.

Continuing from Problem 2, we want to model the situation where a Person can have many accounts (any combination of RegularAccounts and PremiumAccounts). The Person class should have an arraylist of accounts and have these methods:

1. addAccount( a : Account ) – Adds the account a to the Person
2. getAccount( i : int ) : Account – Return the ith No error checking required.

1. getNumAccounts() : int – Returns the number of accounts.
2. getTotalBalance() : double – Returns the total balance added over all the accounts the person has.
3. applyInterest() – applies interest to every account the person has.
5. toString() : string – Returns a string like this:

Num Accounts: 3

 bal = 2234.34 bal = 4523.29 bal = 45.62 Total Balance = 6803.25

Do the following:

2

1. Continue your class diagram from Problem 2 by adding the Person class and any association with the Account class.

1. Write the Person class as described above.
2. Write a tester, java and test your classes thoroughly. Use this Main method:

Person p1 = new Person();

System.out.println(“***Call toString() on Person after 5 accounts are added:”);

System.out.println(p1);

System.out.println();

System.out.println(“***Call getNumAccounts(): ” + p1.getNumAccounts() + “\n” );

System.out.println(“***Call getAccount(1): ” + p1.getAccount(1) + “\n” );

System.out.println(“***Call getTotalBalance(): ” + p1.getTotalBalance() + “\n” );

System.out.println(pa);

System.out.println();

System.out.println(“***Call applyInterest(), then print Person:”);

p1.applyInterest();

System.out.println(p1);

The above test code should output the following:

***Call toString() on Person after 5 accounts are added:

Num Accounts: 5

bal = 2000.0

bal = 3000.0

bal = 200.0

bal = 1000.0

bal = 500.0

Total Balance = 6700.0

***Call getNumAccounts(): 5

***Call getAccount(1): Premium Account: The balance is \$3000.00

***Call getTotalBalance(): 6700.0

Loop over each PremiumAccount and print:

Premium Account: The balance is \$3000.00

Premium Account: The balance is \$500.00

***Call applyInterest(), then print Person:

Num Accounts: 5

bal = 2010.0

bal = 3045.0

bal = 200.0

bal = 1000.0

bal = 507.5

Total Balance = 6762.5

Submission

1. Put your class diagram for problem 3 under the prob3

1. Follow the directions in Lab 1 to zip the folder hw4_FLastname.

Make sure you zip the ENTIRE folder hw4_FLastname!! Submit your zip file to Blazeview by the due date. The name of your file should be: hw4_FLastname.zip.

I will RANDOMLY select one problem for grading. For example, if problem 3 is selected, I will only go to the package/folder prob3 for grading. So make sure all your Java codes are in the correct packages/folders.

• No late submission will be accepted.
• Please exactly follow the naming rules described above. You will be deducted 10 points for incorrect naming.

• Write comments at the beginning of your Java source file(s) to indicate your name, student ID, “CS 1302-A Homework 4”, and the due date.

• It is your responsibility to make sure your programs can compile and run correctly. Please be aware that programs that do not compile may receive ZERO

• When grades are returned to you via BlazeView, you have 7 days to meet with the instructor to discuss on grade changes. After 7 days, the grades are written in stone and can’t be changed after that point.

Problem 1 Hints

1. Create a temporary ArrayList, temp to hold the “unique” integers. Loop through the input ArrayList, list and add to temp when the current integer is not in temp.

1. Use the contains method for the ArrayList class to check to see if an integer is in temp.

1. When you complete the steps above, inside the method, you will have temp which points to the original (input) list and the temp ArrayList which contains just the unique values. How do you update the list to have the values in temp? You might be tempted to simply write:

list = temp;

This will NOT work. Why? First, try it and see. The answer is because Java passes a copy of the reference to the input list. Thus, when you reassign this copy of the reference (the line above), the calling program (main) still maintains a reference to the unaltered list.

So, how do you fix this? Clear the list (clear method) to remove all items from the original list. Then, copy all the values in temp to list (e.g. loop over temp and add each element to list).

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