Description
Objectives
Understand the difference between checked and unchecked exceptions
Throwing/catching checked exceptions
More practice with stacks and queues
Part 1
In this part of the lab you will be experimenting with checked and unchecked exceptions
1. Download the files in the Part1 folder for this lab into your Lab7 folder.
2. Open Exercise1.java and complete the three tasks marked with TODO tags.
3. Open Exercise2.java and complete the five tasks marked with TODO tags.
CHECKPOINT (Ungraded) – Now might be a good time to check-in with the TA if you are aren’t sure you
have completed the tasks as expected. Remember, please don’t hesitate to ask questions if you are unclear
about anything.
Part 2
In this part of the lab you will be inspecting an implementation of the Stack interface that throws
exceptions in place of preconditions.
1. Download the files for this lab into your Lab7 folder.
2. Open Stack.java, StackArrayBased.java and Lab7Part2Tester.java
3. Find the methods in the Stack interface that throw the StackEmptyException
Look at the implementation of these methods in StackArrayBased.java
4. Look at the calls to the Stack methods in Lab7Part2Tester.java and answer the following questions
on paper:
a. Which method calls are wrapped in try/catch blocks
b. What does the tester do within the catch block if it does not expect to reach the catch block?
5. Search for the TODO tag in Lab7Part2Tester.java . In this place, write tests as described to test
whether the exception is thrown when it should case.
6. Update the given implementations of the methods reverseString and doBracketsMatch in
Lab7Tester.java. For each method (one at a time) do the following:
a. Uncomment the code within the method you are working on.
b. Wrap all calls to the methods that throw exceptions in a try/catch block
c. Within the exception catch block, add the line of code appropriate for the logic of the
method. That is, if pop is called on an empty stack, what should the do at that.
CHECKPOINT (Ungraded) – At this point you should be able to compile and run Lab7Part2Tester.java
with testStackUseFunctions uncommented. If this isn’t working, please ask a TA for support. If you
discuss your progress with a TA, make sure you can:
– demonstrate your tests to ensure the exceptions are thrown in the correct case
– how you have used the catch block to control the flow of your program in the methods tested by
testStackUseFunctions .
Part 3
In this part of the lab you will be inspecting an implementation of a generic Queue interface updating it to
throw exceptions in place of the implicit preconditions.
1. Open Queue.java, QueueRefBased.java and Lab7Part3Tester.java. This is a generic
implementation of a Queue.
2. Find the methods in the Queue interface that have the precondition that the Queue must not be
empty. For each of these methods, remove the precondition and change the method so it throws a
QueueEmptyException (provided for you) in place of the precondition. Again, this will cause you
to change your code in multiple places for these updated methods:
a. Signatures of method prototypes in the interface
b. Signatures of method implementations in the class that implement the interface
c. Add code to throw the new exception in the correct case in the method implementations
d. All calls to these methods (in Lab7Tester.java) must be wrapped in a try/catch block.
3. Search for the TODO tag in Lab7Part3Tester.java . In this place, write tests as described to test
whether the exception is thrown when it should be.
REMEMBER: if you get a warning like the following…
Note: Lab7Part3Tester.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
Do as suggested and recompile as follows (it will indicate the line numbers of where the problem code is):
javac -Xlint:unchecked Lab7Part3Tester.java
SUBMISSION (Graded) – Submit the QueueRefBased.java file into the Lab 7 submission page on
ConneX. If you can compile and run Lab7Part3Tester.java with the call to testQueue uncommented, you
are finished!
