Lab #4: Methods
Fall 1999
(To be completed before your lab period, week of October 4)
To introduce methods as a way to organize your program, and to practice the basics of Java programming.
You are to construct a program that is to be used to keep track of the balances of two bank accounts: a savings account and a chequing account. The program will allow for deposits, withdrawals and interest payments to be made on either account.
To begin with, the program will initialize the balance of each account to $0. The program will then continuously prompt the user to select an action. The choices will be to make a deposit, to make a withdrawal, to calculate and deposit interest, or to quit the program. If either of the first three options are selected, the user is asked which account the action is applied to. Each of the deposit, withdrawal and interest calculations actions should be implemented as a separate method that takes the current balance of the account as one of its parameters and returns the modified balance as its result. Each method may have other parameters, in addition to the current balance, if you desire.
You must not use global variables. That is, all variables
referenced must be declared
within the body of a method (between the { and }
characters) or as a parameter to the method (between the ( and
) characters that occur after the method name).
Furthermore, the two variables which you will use to store the current
balance of each account must be declared in the body of
main. You will be penalized if you do not structure your
program in this way.
The deposit method will prompt for a deposit amount, and then return the new account balance. If the deposit is a negative value, ask for a new amount.
The withdrawal method will prompt for a withdrawal value, and return the new account balance. If the withdrawal is negative or greater than the account balance, ask for new amount.
The interest method will calculate the interest earned on the account and return the new balance. Since interest should only be calculated at regular intervals, the interest calculation would be used only by bank employees. To prevent an unauthorized user from asking for interest, this command should be protected by a numerical password. The password number can be a constant hard-coded into your program; when the user requests an interest calculation, your program should prompt the user for the password, and check it.
The two accounts have separate interest rates, which you may hard-code in the program as constants. It is best to pass this as a parameter to your interest method. To calculate the interest, apply the interest rate to the lowest account balance since the last time interest was applied. Note that no interest will be earned the first time, because the opening balance is always zero. However, the bank employee may ask for interest to be credited as often as desired.
An example of the use of the program is shown below. The program should accept either upper or lower case letters to specify termination, e.g., either Q or q for (Q)uit.
--- Bank Account Management Program --- Interaction: (W)ithdrawal, (D)eposit, (I)nterest or (Q)uit? D (S)avings or (C)hequing? s Amount of deposit? 1200 Savings account balance: $1200.00 Interaction: (W)ithdrawal, (D)eposit, (I)nterest or (Q)uit? I Please enter special password: 76567 Interest Access Allowed. (S)avings or (C)hequing? c 2.5% interest applied to $0.00 = $0.00 Chequing account balance: $0.00 Interaction: (W)ithdrawal, (D)eposit, (I)nterest or (Q)uit? d (S)avings or (C)hequing? c Amount of deposit? 2000 Chequing account balance: $2000.00 Interaction:(W)ithdrawal, (D)eposit, (I)nterest or (Q)uit? I Please enter special password: 77887 Interest Access Denied. Interaction:(W)ithdrawal, (D)eposit, (I)nterest or (Q)uit? I Please enter special password: 76567 Interest Access Allowed. (S)avings or (C)hequing? s 1.5% interest applied to $0.00 = $0.00 Savings account balance: $1200.00 Interaction:(W)ithdrawal, (D)eposit, (I)nterest or (Q)uit? I Please enter special password: 76567 Interest Access Allowed. (S)avings or (C)hequing? s 1.5% interest applied to $1200.00 = $18.00 Savings account balance: $1218.00 Interaction:(W)ithdrawal, (D)eposit, (I)nterest or (Q)uit? I Please enter special password: 76567 Interest Access Allowed. (S)avings or (C)hequing? s 1.5% interest applied to $1218.00 = $18.27 Savings account balance: $1236.27 Interaction: (W)ithdrawal, (D)eposit, (I)nterest or (Q)uit? q Savings account balance: $1236.27 Chequing account balance: $2000.00 End of Program
The bank account should not hold fractions of a penny after applying interest, and users should not be allowed to deposit or withdraw fractions of a penny. To properly account for this, store the bank account balance as an integer representing the number of cents in the account (rather than the number of dollars). However, when printing the account balance, it must be printed in dollars (don't worry if you can't print out all of the trailing zeros after the decimal). Likewise, deposits and withdrawals should be done in dollar units. For example, inside your program, convert to cents by multiplying by 100 and casting the result to an int as follows:
double dollars = Stdin.getDouble();
int cents = (int)(dollars * 100);
In addition to the routines Stdin.getInt() and Stdin.getDouble(), which return an int and double type, respectively, you will also need to use Stdin.getChar(), which returns a char type. Just like int and double variables, you can create char variables. These char variables can be compared to other char variables, or compared to single characters which you must place inside single quotes in your program.
The Average.java program from lab 3 used char variables, as does the following example. Notice the use of single quotes to represent one character, and how both Q and q must be handled separately.
// This program writes a prompt to the screen,
// asking the user to type Q to quit. When the
// user finally types Q and ENTER, the program
// prints another message and then quits.
class PromptForQChar
{
public static void main( String[] args )
{
char inputChar;
do
{
System.out.print("Enter Q to quit: ");
inputChar = Stdin.getChar();
} while( inputChar != 'Q' && inputChar != 'q' );
System.out.println("We're done now, thanks for typing Q.");
}
}