CSE 132 (Spring 2015)
Studio 3: Madeoff Bank Heist and a KWIC GUI
Review studio procedures before
starting.
Some guidelines for this week's studio:
- Form groups of no more than four people. If your group
is joined by a fifth person, split into two groups.
- Be sure you are signed in with a TA and that you are cleared before
you leave.
Setup
- Use two computers for this studio, with one open to the studio web page and one
for the eclipse workspace.
- Update your eclipse workspace using the same directions as you used for
studio 1.
- The code from class should appear in the lecture source folder
of
the repository.
Madeoff Bank
In this studio, you will find a
madeoff package, which contains a version of the
Account object you saw in CSE131.
As described in class, the code in this package is not
thread safe.
Most code is by design, in fact, not thread safe. In this case, the lack
of thread safety poses a problem for the bank.
- Follow the steps below to cause the requisite havoc.
- Ask questions and think about what is happening throughout this
part of the studio.
- In the end, you will understand why the code has a race condition and
what you can do to ensure the correct operation of the classes.
- Take a look at the Account object in the madeoff
package.
- Remind yourself how the methods work:
- deposit(int)
- boolean withdraw(int)
- boolean transfer(int, Account)
Do not change the Account class until told to do so, but
do convince yourselves that it works properly.
- The Account's sleep() method simulates the passing of time
by calling
Thread.sleep(int), which causes the thread executing
the method to pause for the specified number of milliseconds.
Such passing of time would happen in the real world on a busy system. We need it
here to create the kind of environment in which real applications run.
- In the Bank class,
you will see a line of code in the runTransactions method:
transactions[i] = null; /* FIXME */
Replace the null with an instance of an anonymous
subclass of Thread that overrides its
run() method.
Review your notes from today's lecture and see the
extra resources (also posted on the
the course calendar):
- In the run() method of the anonymous inner class you created,
write the following statement:
acct1.transfer(TRANSFERAMOUNT, acct2);
- It is likely that eclipse will show you a problem with your code at this
point.
- The yellow lightbulb can help you out, but...
- It is important that you understand what you need to do to fix this.
- Take a look at
- Ask others around you or a TA to explain what's wrong.
- Fix this problem by making the appropriate variable final.
- This part of the studio is set up so that
NUMACCOUNTS Account instances are created, each
with INITIALBALANCE funds in them.
The runTransactions() method executes NUMTRANSACTIONS
transactions,
each transferring TRANSFERAMOUNT funds from
one account to another. The particular accounts are chosen at random. It is
possible that the transfer will take place from and into the same account, which
is fine.
- When the Bank functions correctly and performs
only transfers, the
following should be true:
The sum of all of the Accounts' balances should be
NUMACCOUNTS × INITIALBALANCE
- Go ahead and run Bank as a Java Application.
- It's not really over until the Done message is printed (this
may take about 15 seconds).
- What result do you see?
- Note that for each Thread you create, the code I supplied
calls its run method. What does that method do with respect
to threads?
Let's create a race
- Change the line
transactions[i].run();
to
transactions[i].start();
What is the difference between
.run() and
.start()?
- Run Bank again as a Java Application.
- Qualitatively, how does the program's response time change when
you use .start()? Why is it different?
- In terms of the output, what do you see? Try running the application
many times and describe the behavior.
- What you should be seeing is the bad behavior of a race condition,
as multiple threads compete for access to the various accounts' balances.
Now try to fix the race problems using synchronized
- Based on what you learned in class, you need to put synchronized
on methods in Account to fix this problem:
- Most people will first try putting synchronized on
all the methods. Try that, and let's explore what happens.
If you get tired of waiting, you can terminate the program by clicking
on the red-square stop button.
- Try putting synchronized only on boolean transfer(int, Account) since
that's the only method we really call. What happens and why?
If appropriate, use the debugger to explain what you see.
- OK so where should synchronization be placed, and why?
- Put in the right synchronization and run your code enough times
to convince yourself you get the right answer and there is never deadlock.
Proceed only if you have time and inclination. You're welcome to try the
KWIC GUI part out on your own or later in the semester.
KWIC GUI (time permitting)
As a group, experiment with
WindowBuilder
to design a GUI for the KWIC
lab we started last week.
How should you do this? Design is not something we can do by rote or by
formula. This kind of activity requires creativity and a willingness
to take risks. Put some crazy ideas out there and brainstorm them as
a group.
-
As a point of reference, you saw a (let's go with: "straightforward")
GUI designed in class to give you an idea of what can be done straightforwardly.
I know you can do better.
- Review the videos if you like:
- What swing elements did I use?
- Critical analysis is an important skill in
this course. As a group, come up with at least 3 points of critique on
my design. Be honest and succinct in your
critque, with the goal of giving me feedback
to improve this design.
OK your turn to design a GUI for KWIC. Some notes:
- Think about how you want to make the API of
KWIC available via the GUI:
- Display the list of all Words
- Allow a user to select a Word to display all
Phrases associated
with the Word
- Drop the association between a Word and a Phrase
- Add an association between a Word and a Phrase
- Delete a Word
- Delete a Phrase
- You should browse through the swing online guides:
- You do not need to implement the GUI today, but try to design its
appearance.
- Create a GUI with WindowBuilder:
- Ensure that you are using Eclipse 3.7. WindowBuilder is not part of version 3.5.
- Look over the description of WindowBuilder.
In particular, check out the Swing JFrame Wizard.
- Navigate to your project that contains your kwic package from Lab 2a, even if it is not yet done.
- Create a new JFrame via File -> New -> Other, expand WindowBuilder, expand SwingDesigner, select JFrame. Give it a name, then press Finish.
- Set the Layout to Absolute. You do this in the Design View, click on Absolute from among the Layouts (approx. 1/3 of the way down the Palette), then click on the window being constructed.
- Play! Place a JLabel somewhere in the window. How about a JButton? Move stuff around. Make the GUI look like you want it to.
- Note the ability to move back and forth between the source and the
design with the selectors at the bottom left of the window.
- Make sure you commit if you want to save your work for future use (e.g., for use in Lab 2b).
Demo
When you done with this studio, you must be cleared by the TA to receive credit.
- Commit all your work to your repository
- Fill in the form below with the relevant information
- Have a TA check your work
- The TA should check your work and then fill in his or her name
- Click OK while the TA watches
- If you request propagation, it does not happen immediately,
but should be posted in the next day or so
