Lab 08: Array of Objects

Lab 08: Array of Objects
CSE-021-01

Overview
We will see the power of Object-Oriented Programming (OOP) when we want to create a program that
behaves similar to what we have done before (code reuse). This lab will not be limited to just 3 specialty
cheeses, but to any amount set by the user. Luckily, this does not change anything for the Cheese class, and
we just have to create a shop that contains an array of items to sell, which we will call ShopArr.
Before you get started, read chapters 7.10, 7.11, and 7.12. Answer the Assessment questions as you
encounter them in the next section. The prompts for answering assessment questions are placed
immediately following the material to which the listed questions relate.
Getting Started
After following the import instructions in the assignment page, you should have a Java project in Eclipse
titled Lab21_8. This PDF document is included in the project in the doc directory. The Java files you will
use in this lab are in the src directory.
Copy over RunShop.java and Cheese.java from the previous lab. Your program must produce an
output matching the sample runs given below.
Part 1: Modify RunShop.java (version 2)
In the original RunShop.java (from previous lab), we are creating an instance of Shop class named shop.
Then we call the method run() of this shop object. Now we no longer have an object or class called Shop
and instead, we will be using ShopArr. Import RunShop.java from the previous lab to do this step.
[Answer assessment question 1]
Make the change in RunShop.java file which will allow you to run the newest cheese shop. (same as
answer to Q1)
Part 2: Fill-in ShopArr.java
Everywhere you see comment to “Fill in Code” is where you need to add code to make this program behave
correctly. If it says “Fix Code” you need to change existing code. In most places a sample is provided to
help you get started. The program currently runs, but the behavior is obviously incorrect.
Here is a simpler version of intro() as reference
public static void intro(String[] names, double[]prices, int[] amounts) {
// Special 3 Cheeses
if (names.length > 0) {
names[0] = " Humboldt Fog";
prices[0] = 25.00;
}
if (names.length > 1) {
names[1] = "Red Hawk ";
prices[1] = 40.50;
}
if (names.length > 2) {
names[2] = "Teleme";
prices[2] = 17.25;
}
Lab 08: Array of Objects
CSE-021-01 Points: 20
Random ranGen = new Random(100);
System.out.println("We sell " + names.length + " kinds of Cheese");
if (names.length > 0)
System.out.println(names[0] + ": $" + prices[0] + " per pound");
if (names.length > 1)
System.out.println(names[1] + ": $" + prices[1] + " per pound");
if (names.length > 2)
System.out.println(names[2] + ": $" + prices[2] + " per pound");
for (int i = 3; i < names.length; i++) {
names[i] = "Cheese Type " + (char)('A'+i);
prices[i] = ranGen.nextInt(1000)/100.0;
amounts[i] = 0;
System.out.println(names[i] + ": $" + prices[i] + " per pound");
}
}
We must now split this method into two methods for this lab: init() and intro(). The reason is because
we want to repeat intro() if needed, but creating objects using init() needs to be done only once. So all
the println statements will be moved to intro(). Now take a look at ShopArr.java and the init()
method in it. We see the code is very similar, but the variables have changed. The very first thing we do is
create the array of Cheese pointers since we are given the argument max.
// Create max number of Cheese pointers
cheese = new Cheese[max];
Then you will see the code to handle Humboldt Fog cheese:
if (max > 0) {
cheese[0] = new Cheese();
cheese[0].setName("Humboldt Fog");
cheese[0].setPrice(25.00);
}
Instead of names.length, we now use max in this code.
[Answer assessment question 2]
Also, instead of using three different arrays (names, prices and amounts), we now have only 1 array of
cheeses. So the code is changed to use cheese[0] which points to the first Cheese object in the array. If
we want to change the name then we use a mutator setName, which exists inside the Cheese object
(cheese[0]), that we access using the “.” operator. We instantiate Humboldt Fog using default constructor
with 0 arguments followed by invoking two mutators. Red Hawk is instantiated with a 1-argument
constructor followed by invoking only one mutator. And finally, Teleme uses a 2-argument constructor, so
no mutator calls are necessary. Note that you must use the corresponding accessor method calls in other
parts of the code to get to the value of the variables set by the mutators.
[Answer assessment questions 3, 4 and 5]
Now you will need to implement the for-loop in init(). The original loop is as follows:
for (int i = 3; i < names.length; i++) {
names[i] = "Cheese Type " + (char)('A' + i);
prices[i] = ranGen.nextInt(1000)/100.0;
amounts[i] = 0;
}
You must figure out the transformations needed in the for-loop to work with a single cheese array instead
of 3 arrays, as shown by the code already inside init(). You can assume the amount is already set to 0 for
each cheese so the loop doesn’t need to set it again to 0.
[Answer assessment question 6]
We have also implemented the basic version of ShopArr constructor which just invokes init method with
a fixed number, 10. You must fill-in the 1-argument constructor which will invoke init using the max
parameter instead.
[Answer assessment question 7]
Now implement intro(Scanner), itemizedList(), calcSubTotal() and discountSpecials() so
they work for an array of cheese pointer. The methods printSubTotals() and printFinalTotal()
should be identical to Lab 07.
[Answer assessment questions 8 and 9]
Part 3: Modify RunShop.java (version 3)
Now notice that there are two constructors for ShopArr available and version 2 of RunShop (from Part 1) is
only calling the default constructor with no arguments. So, the program will always create 10 cheeses to sell.
We will need to make use of the second constructor which takes an argument max and sets the amount of
cheeses to sell.
Modify RunShop so it asks the following question to the user and then pass the number user enters to the
ShopArr constructor. So the program now starts as follows:
Enter the number of Cheeses for shop setup: 12
We sell 12 types of cheese, in 0.5 lb packages:
Everything should work as it did before, now you can just change the number of cheese from 10 to any
amount you want (including 0 but not negatives).
[Answer assessment question 10]
Part 4: (Assessment) Logic Check and Level of Understanding
Create a Word document or text file named Part4 that contains answers to the following:
1) What are the minimal changes required to instantiate ShopArr and invoke run() on it?
2) We can also use a <something>.length instead of max. What is the valid <something> to use in
ShopArr.java?
3) How can we tell which instantiation (new Cheese) corresponds to which constructor definition inside
the Cheese class?
4) How can we identify a mutator method call?
5) What would be the result if we added this line right after Teleme is created:
cheese[2].setName("Wrong Name"); ?
6) Why is the init() method both private and void?
7) What is the difference between ShopArr() and ShopArr(int max) constructors.
8) How can we figure out the number of required iterations for each loop?
9) Should we pass in Cheese array pointer (cheese[]) as arguments into calcSubTotal or
itemizedList? (Why or why not)
10) What value will be printed by RunShop for “Ran with Cheese Total”? (fixed number or a formula)
Sample Runs (user input shown in green, with each run separated by a dashed-line):
-------------------------------------------------------------------------------SAMPLE RUN 1
1 Enter the number of Cheeses for shop setup: 0
2 We sell 0 kinds of cheese, in 0.5 lb packages:
3
4
5 Display the itemized list? (1 for yes): 1
6 No items were purchased.
7
8 Original Sub Total: $0.00
9 Specials...
10 None -$0.0
11 New Sub Total: $0.00
12 Additional 0% Discount: -$0.0
13 Final Total: $0.00
14
15 Do you wish to redo your whole order? (1 for yes): 0
16
17 Thanks for coming!
18 Ran with Cheese Total: 0
-------------------------------------------------------------------------------SAMPLE RUN 2
1 Enter the number of Cheeses for shop setup: 1
2 We sell 1 kinds of cheese, in 0.5 lb packages:
3 Humboldt Fog: $25.0 per pound
4
5 Enter the amount of Humboldt Fog in lb: 1
6
7 Display the itemized list? (1 for yes): 1
8 1.0 lb of Humboldt Fog @ $25.00 = $25.00
9
10 Original Sub Total: $25.00
11 Specials...
12 Humboldt Fog (Buy 1 Get 1 Free): -$12.50
13 New Sub Total: $12.50
14 Additional 0% Discount: -$0.0
15 Final Total: $12.50
16
17 Do you wish to redo your whole order? (1 for yes): 1
18
19 We sell 1 kinds of cheese, in 0.5 lb packages:
20 Humboldt Fog: $25.0 per pound
21
22 Enter the amount of Humboldt Fog in lb: 0
23
24 Display the itemized list? (1 for yes): 1
25 No items were purchased.
26
27 Original Sub Total: $0.00
28 Specials...
29 None -$0.0
30 New Sub Total: $0.00
31 Additional 0% Discount: -$0.0
32 Final Total: $0.00
33
34 Do you wish to redo your whole order? (1 for yes): 0
35
36 Thanks for coming!
37 Ran with Cheese Total: 1
-------------------------------------------------------------------------------SAMPLE RUN 3
1 Enter the number of Cheeses for shop setup: 4
2 We sell 4 kinds of cheese, in 0.5 lb packages:
3 Humboldt Fog: $25.0 per pound
4 Red Hawk: $40.5 per pound
5 Teleme: $17.25 per pound
6 Cheese Type D: $9.15 per pound
7
8 Enter the amount of Humboldt Fog in lb: 4.5
9 Enter the amount of Red Hawk in lb: 4.5
10 Enter the amount of Teleme in lb: -3
11 Invalid input. Enter a value >= 0: 1.7
12 Invalid input. Enter a value that's multiple of 0.5: -4
13 Invalid input. Enter a value >= 0: 1.9
14 Invalid input. Enter a value that's multiple of 0.5: 1.5
15 Enter the amount of Cheese Type D in lb: 10
16
17 Display the itemized list? (1 for yes): 1
18 4.5 lb of Humboldt Fog @ $25.00 = $112.50
19 4.5 lb of Red Hawk @ $40.50 = $182.25
20 1.5 lb of Teleme @ $17.25 = $25.88
21 10.0 lb of Cheese Type D @ $9.15 = $91.50
22
23 Original Sub Total: $412.13
24 Specials...
25 Humboldt Fog (Buy 1 Get 1 Free): -$50.00
26 Red Hawk (Buy 2 Get 1 Free): -$60.75
27 New Sub Total: $301.38
28 Additional 15% Discount: -$75.34
29 Final Total: $226.03
30
31 Do you wish to redo your whole order? (1 for yes): 0
32
33 Thanks for coming!
34 Ran with Cheese Total: 4
-------------------------------------------------------------------------------SAMPLE RUN 4
1 Enter the number of Cheeses for shop setup: 12
2 We sell 12 kinds of cheese, in 0.5 lb packages:
3 Humboldt Fog: $25.0 per pound
4 Red Hawk: $40.5 per pound
5 Teleme: $17.25 per pound
6 Cheese Type D: $9.15 per pound
7 Cheese Type E: $2.5 per pound
8 Cheese Type F: $8.74 per pound
9 Cheese Type G: $9.88 per pound
10 Cheese Type H: $2.91 per pound
11 Cheese Type I: $6.66 per pound
12 Cheese Type J: $0.36 per pound
13 Cheese Type K: $2.88 per pound
14 Cheese Type L: $7.23 per pound
15
16 Enter the amount of Humboldt Fog in lb: 1.5
17 Enter the amount of Red Hawk in lb: 2.2
18 Invalid input. Enter a value that's multiple of 0.5: 2.5
19 Enter the amount of Teleme in lb: 0
20 Enter the amount of Cheese Type D in lb: 0
21 Enter the amount of Cheese Type E in lb: 0
22 Enter the amount of Cheese Type F in lb: 0
23 Enter the amount of Cheese Type G in lb: 8
24 Enter the amount of Cheese Type H in lb: 10
25 Enter the amount of Cheese Type I in lb: 0
26 Enter the amount of Cheese Type J in lb: 0
27 Enter the amount of Cheese Type K in lb: 0
28 Enter the amount of Cheese Type L in lb: 0
29
30 Display the itemized list? (1 for yes): 1
31 1.5 lb of Humboldt Fog @ $25.00 = $37.50
32 2.5 lb of Red Hawk @ $40.50 = $101.25
33 8.0 lb of Cheese Type G @ $9.88 = $79.04
34 10.0 lb of Cheese Type H @ $2.91 = $29.10
35
36 Original Sub Total: $246.89
37 Specials...
38 Humboldt Fog (Buy 1 Get 1 Free): -$12.50
39 Red Hawk (Buy 2 Get 1 Free): -$20.25
40 New Sub Total: $214.14
41 Additional 10% Discount: -$21.41
42 Final Total: $192.73
43
44 Do you wish to redo your whole order? (1 for yes): 1
45
46 We sell 12 kinds of cheese, in 0.5 lb packages:
47 Humboldt Fog: $25.0 per pound
48 Red Hawk: $40.5 per pound
49 Teleme: $17.25 per pound
50 Cheese Type D: $9.15 per pound
51 Cheese Type E: $2.5 per pound
52 Cheese Type F: $8.74 per pound
53 Cheese Type G: $9.88 per pound
54 Cheese Type H: $2.91 per pound
55 Cheese Type I: $6.66 per pound
56 Cheese Type J: $0.36 per pound
57 Cheese Type K: $2.88 per pound
58 Cheese Type L: $7.23 per pound
59
60 Enter the amount of Humboldt Fog in lb: 0
61 Enter the amount of Red Hawk in lb: 0
62 Enter the amount of Teleme in lb: 12
63 Enter the amount of Cheese Type D in lb: 0
64 Enter the amount of Cheese Type E in lb: 1
65 Enter the amount of Cheese Type F in lb: 2
66 Enter the amount of Cheese Type G in lb: 3
67 Enter the amount of Cheese Type H in lb: 0
68 Enter the amount of Cheese Type I in lb: 0
69 Enter the amount of Cheese Type J in lb: 5
70 Enter the amount of Cheese Type K in lb: 0
71 Enter the amount of Cheese Type L in lb: -3
72 Invalid input. Enter a value >= 0: 1.1
73 Invalid input. Enter a value that's multiple of 0.5: 4
74
75 Display the itemized list? (1 for yes): 0
76
77 Original Sub Total: $287.34
78 Specials...
79 None -$0.0
80 New Sub Total: $287.34
81 Additional 15% Discount: -$71.84
82 Final Total: $215.51
83
84 Do you wish to redo your whole order? (1 for yes): 0
85 Thanks for coming!
86 Ran with Cheese Total: 12
Specification Compliance
The following are some additional instructions to make sure your project complies with specifications:
1. Your program must produce an output that exactly resembles the Sample Output shown above,
including identical wording of prompts, spacing, input locations, etc.
2. Your program must ensure the following:
a. Your program should not display items that are not bought (amount is 0) when listing them out [cf.
Sample Run 4, Lines 31-34]. If no items are purchased, then a special message is displayed [cf.
Sample Run 2, Line 35].
b. If no discounts are applied, a special message is displayed [cf. Sample Run 4, Line 79].
3. Your program must check for invalid inputs when entering the amounts [cf. Sample Run 3, Lines 8-15].
4. Before you submit, in Eclipse, type CTRL-A (to select everything) followed by a CTRL-I (to fix
indentation) on each of your java programs. In MacOS the corresponding keystrokes are Cmd-A
followed by Cmd-I.
What to hand in
When you are done with this lab assignment, submit all your work through CatCourses.
Before you submit, make sure you have done the following:
• Attached the file named Part4 containing answers to Assessment questions (1 – 10).
• Attached the ShopArr.java and RunShop.java files.
• Filled in your collaborator’s name (if any) in the “Comments…” text-box at the submission page.
Also, remember to demonstrate your code to the TA or instructor before the end of the grace period.