Description
Learning outcomes
When you have completed this assignment, you should have become (re-)acquainted
with:
• how to create a one-dimensional (i.e., 1D) array;
• how to read from and write to array elements, using both explicit and
computed index values;
• how to create instances of custom classes;
• how to compile, execute and test a multi-class program;
• how to use visibility modifiers such as private and protected.
In addition to these you will be introduced to:
• how to read and use a method specification.
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The task for this assignment
Problem description
For this assignment you must complete the implementation of some methods
contained within three provided classes in a way that satisfies the specifications
given for methods in the classes. The three classes are:
• Student.java
• GradStudent.java
• Course.java
A fourth class has also been provided:
• A1test.java
and its purpose is to use the results of your work. That is, A1test will test your work
in Student, GradStudent and Course for basic correctness.
Therefore one of the first steps you should take after downloading all four sourcecode files is to compile and run the test program. Assuming all files are in the same
directory, you will do this:
$ javac A1test.java
$ java A1test.java
Testing of ‘Student’ class (basic)
Failed test: 1 at line 73
The tester program indicates here that your implementation – which, of course, has
yet to be started! – fails in the very first test. That test was exercised at line 73 in
A1test.java. If you read this line and the few before it, you’ll see that line 73 is a check
on whether or not the student ID given in the constructor for a student object is
indeed what was returned by a call to getId() on that object.
The purpose of some tests will be quite clear and obvious, some will require a bit of
thought to understand, and others are more complex only because of the code used
to implement the test (i.e., the “stress” tests). However, reading code is as important
a task as writing code. Therefore by reading the tests as they pass (and fail) along
with comments provided before the empty methods in Student, GradStudent and
Course, you’ll slowly but surely determine what is required to pass all tests.
A word of caution: It is possible for some tests to pass at first only to then fail after
additional code later completed. This is not unusual and is often a sign that your
existing code has a bug that is only now exercised by what the newer code has
constructed. Once you find and fix the bug, the earlier test will again start to pass.
When we evaluate your work, it is the first failed test that will matter most for us (i.e.,
we do not cherry-pick test by ignoring earlier failed tests while accepting later
passing tests). Tests after the first failed test are themselves considered to have failed.
There are 51 52 tests and your code is expected to pass them all.
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Suggested implementation strategy
1. Start your work by attempting to complete Student.java.
2. First implement the constructor that takes two parameters.
3. Then implement getCredits(), getName() and getId(). Recompile Student.java.
(From this point onwards the text will not indicate when you should
recompile. I assume you can determine this for yourself.)
4. Now re-run the tester. Assuming your work is correct, you will have passed
tests 1, 2 and 3. The first failure will now be test 4 (i.e., on line 78).
5. Implement setCredits(). Again assuming your work is correct, you will have
passed the first four tests. The next failure, however is an exception – you will
be told a NullPointerException occurred at line 81 in A1test.java.
6. If you look at that line, you’ll see it occurs right after a call to the Student
constructor that takes three parameters. Given what you’ve written so far,
why might this be the case?
7. Assuming you have determined what caused the error in step 6 and written
the appropriate additional code, the first seven tests will pass, and now the
first failing test is test 8.
8. Implement setName(). Re-run the tester, and now the first failing test will be
10.
9. Implement equals(). (Be sure the read the specification carefully, and
remember comparing strings with “==” can often give false negatives.) After
this is correctly completely, the first failing test will be 12.
10. Implement toString(). After this is correctly implemented, all of the first set of
tests will have passed (i.e., the first 15 tests).
At this point you will have completed the implementation of Student.java. Proceed
with GradStudent.java, and then Course.java. (Hint: When implementing a class
always first complete its constructors.)
Note that some tests are more complicated than others.
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Files to submit (three in total):
a. Student.java
b. GradStudent.java
c. Course.java
Submit these using conneX. Ensure you actually submit the files and do not just
submit a draft assignment.
Grading scheme
Requirement Marks
All three java files compile without errors or warnings 2
Code passes the first set of test cases (1 to 15) 2
Code passes the second set of test cases (16 to 28) 3
Code passes the third set of test cases (29 to 33) 3
Code passes the fourth set of test case (34 to 42) 3
Code passes the fifth set of test cases (43 to 49) 2
Code passes the sixth set of test cases (50 to 52) 3
Code uses follows the posted coding conventions on commenting. 2
Total 20
Note: Code submitted must be written using techniques in keeping with the goals of
the assignment. Therefore passing a test is not automatically a guarantee of getting
marks for a test (i.e., your solution must not be written such that it hardcodes results
for specific tests in A1test.java yet would be unable to work with similar tests when
different data is used).
In order to obtain a passing grade for the assignment, you must satisfy at least the
first four requirements by passing all of their test cases.
