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HOMEWORK MEMENTO
OBJECTIVE: Learn how to use the Memento design pattern and get practice writing binary
objects out to a file.
INTRODUCTION: Your text illustrates how to write multiple objects out to a binary file using stream
I/O. In the text, those objects are arranged in some collection class, say an array
or ArrayList, and your code writes out the whole array or ArrayList to the file in
one statement. This approach will not scale well if you get a large collection of
large objects. It is better to store instances of a given object out to a file one at a
time if you do not know for sure how many you will eventually need to write.
In many of the articles online regarding the Memento pattern, the state shows
up as a String. The authors do that to make the example code simpler, and
hopefully easier to understand. But you have to remember that generally
speaking, the state of an object is the combination of the value of all of its
instance variables. The instances of a large complex class could each have a very
complex state indeed.
For this homework assignment, we are going to simulate a somewhat contrived
personnel records application. Each time that you run your application it will
store multiple sets of values for the same person. In our simplified world, their
first and last name never changes, but their hair color, height, and weight may
change from one set of “readings” to the next. For instance, I have been 5’10”
for quite some time, and I have not started to lose height yet. So my height is
pretty stable. But my hair has gone from auburn to gray, to salt and pepper to
nearly white. During that same span of time, my weight has gone up and down
some as well. So there will be multiple instances of Person for me, each one
reflecting my statistics at a given time.
In this homework assignment the Caretaker writes each memento to your binary
output stream individually, rather than all at once. The MementoRunner class
will prompt the user for a fresh set of values for the Person (more on that in a
minute) and make a PersonMemento instance from that Person instance and
then store that PersonMemento in your stream object file.
Then, once all of the PersonMementos have been written to disk, you will read
all of those PersonMemento instances from start to finish, and find the one
which has the lowest weight. Then, in a separate statement, I want you to prompt
the user for a weight to search for, then find the Memento whose corresponding
Person instance has that weight and return the first Memento that you find with
that weight.
PROCEDURE:
1. Start with the Person class. This class performs the role of the Originator in the Memento design
pattern. The code for that is here.
a. You need to add a save() method that creates an instance of PersonMemento (more
on that in a minute) from the current Person instance.
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CECS 277 HOMEWORK MEMENTO
b. You need to add a restore (PersonMemento archive) method that returns an
instance of Person that has the same state as the Person instance stored in the supplied
PersonMemento.
2. Then write your PersonMemento class, which performs the duties of the Memento class in the
design pattern:
a. A constructor that takes just one argument: the Person instance that you want to
preserve into an instance of PersonMemento.
b. A getSavedPerson method that returns an instance of Person with the same values
as the Memento.
c. Remember that your Caretaker class will write instances of PersonMemento out to
a file output stream file, so that means that you must implement the serializable
interface.
3. Then write your Caretaker class:
a. The Caretaker class does all of the I/O with your Memento file that has all of your
Memento instances (not Person instances) in it. Once you establish an instance of
Caretaker, that object has the same file that it writes to and reads from.
i. The caretaker class could just randomly come up with a file name for the
mementos written out to disk, but its safer to prompt the user for that file name.
ii. Caretaker will have a single constructor that takes in a file name for the binary file
that it uses to write to/read from.
1. You prompt the user for the name of that file in your runner (Main)
method.
2. The caretaker will need to first create a FileOutputStream from that file
name, then use that FileOutputStream to create a new ObjectOutput
Stream.
3. The caretaker will also need to create a new FileInputStream that points
to the same binary file as the FileOutputStream, and an
ObjectInputStream from that FileInputStream.
4. Both the FileInputStream and FileOutputStream need to be member
variables in your caretaker instance.
5. The addMemento will always append the new memento to the end of
the binary file that the caretaker “owns”.
6. Each time the caretaker performs a getMemento, you will need to:
a. Close the binary file that you have been writing your Mementos
to.
a.b.Create a new ObjectInputStream pointing to the binary file so
that you can start at the front of the file again when you start
reading in mementos.
b. Write your addMemento method to write out a Memento instance.
c. Write two methods to search through a file of Mementos. Both of theseBoth methods
are called getMemento:
i. The first one has no arguments, and simply returns an instance of
PersonMemento that has the lowest weight.
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CECS 277 HOMEWORK MEMENTO
ii. The second getMemento method takes an integer weight as its only argument,
and returns the first instance of PersonMemento that it finds in the file that
has a weight that matches the input weight. If none of the Mementos have
exactly the weight requested, then return a null pointer.
4. Finally, write a driver class that:
a. Prompts the user for the name and path of the file that they will use for storing their
PersonMemento objects.
b. Goes into a loop, prompting the user for the Person characteristics (height, weight, …) at
various times.
c. Uses getMemento to find the skinniest of the PersonMementos that have been written
to disk.
d. Uses getMemento to find the first PersonMemento that matches the weight that you give
it.
SAMPLE OUTPUT:
Note that I used JFileChooser to prompt the user for the file name.
prompting you for persons:
Enter the person’s last name: Berry
enter the person’s first name: Blue
0: BLACK
1: BLONDE
2: RED
3: AUBURN
4: SALT_AND_PEPPER
5: GREY
6: WHITE
7: BALD
Please enter the # corresponding to the hair color: 1
You entered color: BLONDE
Person’s height in feet: 5
And the inches? For instance, 5’10” would be 10: 11
Their weight in pounds: 132
Name: Berry, Blue, Hair Color: BLONDE, Height:5’11, Weight #: 132
Are we done here (Y/N)?: N
0: BLACK
1: BLONDE
2: RED
3: AUBURN
4: SALT_AND_PEPPER
5: GREY
6: WHITE
7: BALD
Please enter the # corresponding to the hair color: 5
You entered color: GREY
Person’s height in feet: 5
And the inches? For instance, 5’10” would be 10: 10
Their weight in pounds: 136
Name: Berry, Blue, Hair Color: GREY, Height:5’10, Weight #: 136
Are we done here (Y/N)?: N
0: BLACK
1: BLONDE
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CECS 277 HOMEWORK MEMENTO
2: RED
3: AUBURN
4: SALT_AND_PEPPER
5: GREY
6: WHITE
7: BALD
Please enter the # corresponding to the hair color: 6
You entered color: WHITE
Person’s height in feet: 5
And the inches? For instance, 5’10” would be 10: 9
Their weight in pounds: 150
Name: Berry, Blue, Hair Color: WHITE, Height:5’9, Weight #: 150
Are we done here (Y/N)?: Y
Skinniest version: Name: Berry, Blue, Hair Color: BLONDE, Height:5’11, Weight
#: 132
What weight do you want to search for?136
Sought after version: Name: Berry, Blue, Hair Color: GREY, Height:5’10,
Weight #: 136
Completed satisfactorily.
WHAT TO TURN IN:
• MementoRunner.java
• Person.java
• PersonCaretaker.java
• PersonMemento.java
• console.txt
• The UML diagram class for your project.

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