Lab 3.2 ChangeMachine
Assignment:
Your goal is to simulate a change machine that keeps track of currency (bills and coins) and dispenses efficient change during a transaction.
Create a ChangeMachine class
Add private instance variables to keep track of
- Number of pennies, nickels, dimes, quarters
Notes:
- Students often want to add an instance variable for the total amount of money but this is a bad idea. You should calculate the total in a method that returns the total instead of storing the total in a variable. Why? Because the total can change depending on money added/taken out of the change machine. You should calculate the total on demand whenever it's needed using a helper method rather than try to update a variable to keep up with the current total as the program changes over time. Otherwise your total variable can get out of sync with the current total.
Add a default constructor that sets the following default values:
50 pennies
40 nickels
30 dimes
20 quarters
Add a second constructor that takes parameters specifying how many of each coin to start with.
Add method(s) that add more change to the machine. You can do this using a single method that accepts each type of coin or you can have separate methods for adding more of each type of coin separately.
Example usage (assuming a ChangeMachine named 'machine' has been created)
machine.addPennies(45); // Adds 45 more pennies to the machine
Create a method that will print the amount of each coin in the ChangeMachine. Use tab characters \t to get the formatting lined up. The output should look something like this:
The change machine contains:
Quarters: 20
Dimes: 30
Nickels: 40
Pennies: 50
Add a method that RETURNS the total amount of money in the ChangeMachine. The return type for this method should be double.
Read Lesson 4, Page C for a quick review of writing methods that return a value.
Your method should return a double and not have any parameters.
Example:
public double calculateTotal() { }
Inside the method body you should calculate the total and return it.
Example:
double total = 0;
total += // value of pennies
total += // value of nickels
…etc
return total;
- If you keep track of the total cents instead of dollars, you will avoid rounding errors. You can still convert it to dollars as a double at the end.
Add a method that PRINTS the total amount of money in the ChangeMachine. The return type for this method should be void.
Example output:
The change machine total is $17.28
Note:
If the second decimal place is a zero, the output will display as something like $15.2 That's ok.
You can either recalculate the total in this method or (better yet) you can call upon your calculateTotal() method and then print the returned value.
Add a dispenseChange method that calculates and dispenses efficient change for a desired amount of money. Your method should be void and print the output in the format shown below.
For example, if a user wants change for $5.42 then the machine should give back
Change for $5.42
Quarters: 21
Dimes: 1
Nickels: 1
Pennies: 2
If efficient change can be made then print the format shown above and subtract the corresponding number of coins from each instance variable in the ChangeMachine.
If efficient change cannot be made (for example, there aren't enough pennies or nickels) then print out an error message and do not reduce any of the instance variables.
Insufficient coins! Cannot make efficient change for $5.42
- Finally, write a Driver class that creates an instance of your ChangeMachine and tests each method. For example, if you create a default ChangeMachine and print the total, it should be $87.1 If you then get change for $6.83, you should have fewer quarters, dimes, and pennies. Make sure the number of coins and the total are always correct after making a transaction. Test each method rigorously.
Your files must be named appropriately. For example, P3_Wang_Michael_ChangeMachine.java and P3_Wang_Michael_Driver.java
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