Java project easy1

Computer Science 110 Introduction to Algorithms and Programming: Java

Programming Project #5 – Classes and Objects

Due Date: April 17, 2014

You will create 3 new classes for this project. The first class, named Book will

represent a printed book, like the textbook for this class. The second class, named

Student will represent a generic CSUN student. The third class will be one that you

invent on your own.

Design Your Classes First

Create three (3) UML diagrams for your three classes. Two of the classes are

assigned by the instructor (see the paragraph above) and one you must invent. Choose

as the third class, a singular noun that identifies something you know very well or

love doing. If soccer is your favorite sport, create a class named Soccer. If you surf,

create a class named Surfboard. Don’t overthink it, just come up with the 3 most

important data members (i.e. instance variables) that describe the class/object you

want to build and then write headers for 2 constructors, 3 get methods, 3 set

methods and a toString() method for each diagram.

Next to each UML diagram, decide on a default value, minimum value and a

maximum value for each NUMERIC variable. For example, a Shoe class might have

a variable called size. This size variable might have a default value of 0, a minimum

size of 1 and a maximum size of 15. A String variable might have a default value of

null and a minimum and maximum length for that String. For example, a Computer

class might have a variable called brand. This brand variable might have a default

value of null, a minimum string length of 3 and a maximum length of 20. Please DO

NOT use the same 3 data types for any classes’ global variables. That is, do not

make them all “int” or all “String”. It is acceptable to define two variables with the

same data type, so long as the third one has a different data type.

Implement (Code) Next

Once you have designed your classes on paper, create a jGrasp project named

Project5. Within Project5, create a Java file for EACH of the three classes. For

example, add to your project a new file called Book.java and then create the new class

from scratch in that file. Use your UML diagrams as the guideline for writing the

code. The variables and methods from the diagrams will be part of each of your new

classes. Make sure ALL your variables are declared to be private and do not make

them static. Also, make sure you follow the Java naming conventions listed in your

textbook by capitalizing the first letter of each word in the class name. It is important

to follow standardized naming conventions to make your programs easy to read.

Protect Your Data!

Objects store data or information! All class-level variables should be declared as

private, to protect data from access by code outside of the class. Think back to the

BankAccount example that was demonstrated in lecture—the public variables in that

class permitted a main() method in another class to “reach in” and take $2 million out

of myAccount. Do not make the same mistake; ALWAYS protect the data in your

objects by making them private.

Also, never allow bad data to be stored in your objects! In each “set” method,

make sure the value passed to the method is within a range, greater than or equal to a

minimum and less than or equal to a maximum. For Strings, you may check the

length of the String. Each “set” method should have some sort of “if-else” statement

which assigns the data when it is good and print an informative message when an

incorrect value is passed. A Shoe class setSize() method would assign the value “10”

to the size global variable when it is passed to the method, but it would print a

message stating “Shoe size must be between 1 and 15” and NOT change the global

variable when values like “437” are passed to the method. The private variable

declarations build a wall around your data, and the “set” methods are the

“gatekeepers” that allow only “good” information in. Your constructor that takes

arguments and assigns values to global variables should use the “set” methods so you

DO NOT have to repeat the same checks in the constructor. The NO-ARGS

constructor can go ahead and directly set the default values into the global variables.

Test Last

For each class, create a main method that will declare, build and use an object of that

class. So the main() method in Book.java will declare, build and use a Book object,

and the other two classes will do the same. Use the command-line interface to ask

the user to input a value for EACH global variable. Call a constructor or the set

methods and insert that information into the object. Once the data is inserted, use the

object to call the toString() method (using the dot operator) and print the object to

the console. You will be writing THREE main methods, one for each class. When

you test, make sure your set methods DO NOT allow bad data into the object. Try

to make it fail, see if you can sneak bad values into the variables.

To insure you complete each class, use this checklist:

_____ Three global variables (not the same type)

_____ Two constructor methods

_____ Three “get” methods

_____ Three “set” methods

_____ One 'toString' method

_____ One main method that creates an object, assigns values, and prints the

object

Extra Credit (3 points) - See if you can get jGrasp to build your project into one

compressed 'Project5.jar' file. Build a NEW project/program that has

NOTHING to do with Project5 and is a separate directory/folder. Add your jar

file to the CLASSPATH for this project. Create a test program within this new

project. Build and use objects from all three classes in this program.