Description
Exercise 1 – Accessing static vs. non-static variables
1. Open VariableTest.java in Eclipse and examine the code. Notice the difference between
sNum and iNum.
2. Add a test harness main (String[] args) method at the bottom of this class. Within
it, add two consecutive print lines: one printing out iNum and one printing out sNum.
3. What does the IDE / compiler say about these lines? Why is one of them valid but the
other invalid? Comment out the offending line.
4. Create an object and print out the iNum value of that object.
Exercise 2 – Method parameters
When a primitive variable is declared, it is allocated a memory location. When that primitive
variable is initialized (for example, with the value of 5) the value at its memory location takes on
the value of 5. In contrast, when a reference variable is declared and initialized, the value at its
memory location takes on the value of another memory location. Given this information, can you
explain why the following demo works the way that it does? If you are confused, try drawing the
memory locations and their values on paper.
CS1027
LAB 8 Computer Science Fundamentals II
1. Open MemoryDemo.java and examine the code but do not run it.
2. As you examine the code visually, write down the results you expect it to print out.
3. Once you have written the expected results, run the program to see the actual results.
Were you correct? If not, review the paragraph at the start of this exercise to try to
understand the reason for these results.
Exercise 3 – String equality
A string created without the use of the new operator is called a string literal (i.e. String s = “hi”).
String literals are objects, but the Java compiler will not create two copies of the same string
literal. The string literals are saved into a special memory pool and duplicates point to the same
literal to reduce the amount of memory that a Java program uses.
1. Open StringCompare.java but do not run it.
2. Carefully read through the 6 different test cases written in the test harness. Notice that
the first 3 cases use == and the last 3 call the equals() method. Notice also that in each
of these sets of 3 cases, the Strings are initialized slightly differently.
3. As you examine these 6 different String comparison cases, write down the results you
expect from each of the cases (true or false).
4. Once you have written expected results, run the program to see the actual results. Were
you correct? For any cases in which your expected result was incorrect, review the code
to understand why this occurred. Review the paragraph on string literals at the start of
this exercise if you are confused by these results.
Exercise 4 – Create a receipt program
1. Open Product.java in Eclipse and examine the code.
2. Create a new class called Receipt.
3. The only instance method you need to implement in Receipt.java is a constructor with
the following signature: public Receipt (Product[] cart) { }
4. In the constructor, loop through each of the products in the cart array and display each
one on its own line with clean formatting. Each line must include the product’s name,
code, cost, and the after-tax cost. Use the following hints and guidelines:
Align the print lines in a table-like structure so that each row (line) is a single
product and each column is each of the attributes (name, code, etc.)
Use String.format() or System.out.printf() with “%” to help with the
alignment. Refer to the zyBook section 9.2 for a refresher.
CS1027
LAB 8 Computer Science Fundamentals II
If you call prod.getTax() (assuming prod is the Product variable), it will be
underlined in yellow to indicate a warning. This means it will technically still
compile and run with this line, but it is not recommended. How is this method
different from the other getters in Product.java? How should this type of method
be called? Call it the proper way so there are no warnings.
5. Add a print line before the loop to display header labels for each of the columns (product
name, code, cost, and after-tax cost) with the same table-like alignment.
6. Add a line after the loop that displays the grand total and keep it aligned with the column
of the individual product’s after-tax costs.
7. Add a test harness main (String[] args) method at the bottom of this class. Within
it, initialize at least 3 different Product objects and create a Product array containing
these items. Then initialize a new Receipt object with the Product array parameter.
8. View an example of the expected output (note that you can use any product names,
codes, and costs so your output may not be identical to this one).
Submission
When you have completed the lab, navigate to the weekly module page on OWL and click the
Lab link (where you found this document). Make sure you are in the page for the correct lab.
Upload the files listed below and remember to hit Save and Submit. Check that your submission
went through and look for an automatic OWL email to verify that it was submitted successfully.
Rules
Please only submit the files specified below. Do not attach other files even if they were
part of the lab.
Do not ZIP or use any other form of compressed file for your files. Attach them
individually.
Submit the lab on time. Late submissions will receive a penalty.
Forgetting to hit “Submit” is not a valid excuse for submitting late.
Submitting the files in an incorrect submission page will receive a penalty.
You may re-submit code if your previous submission was not complete or correct,
however, re-submissions after the regular lab deadline will receive a penalty.
Files to submit
VariableTest.java
Receipt.java
