P7 GENERATING PHILOSOPHY

PROGRAMMING II
Department of Computer Sciences
Pair Programming is NOT allowed for this assignment
This Assignment involves developing increasingly general (eventually using Java Generics)
Generators that implement the Iterable and Iterator interfaces within the Java API. Rather than
iterating through a pre-existing collection of data, your code will be generating this data on
demand. The final generalization of this pattern will be used to explore the structure of Wikipedia
and the significance of its Philosophy page.
OBJECTIVES AND GRADING CRITERIA
The main goals of this assignment include giving you practice and experience with both Generics
and Iterators in Java. You will implement the Iterable and Iterator interfaces of the Java API, and
practice generalizing your code to be useful in a wider variety of applications.
20
points
4 zyBooks Tests: automated grading test results are visible upon submission, and allow
multiple opportunities to correct the organization and functionality of your code. Your
highest scoring submission prior to the deadline will be recorded.
10
points
2 Hidden Tests: automated grading tests are run after the assignment’s deadline. They
check for similar functionality and organizational correctness as the zyBooks Tests. But
you will NOT be able to resubmit corrections for extra points, and should therefore
consider and test your own code even more thoroughly
20 Final Submission Commenting, Style and Organization: human graders will review the
P7 GENERATING PHILOSOPHY
LECTURE NOTES
points commenting, style, and organization of your final submission. They will be looking for
clear comments and consistent style that make appropriate use of java constructs,
conforms to this write-up and the CS300 Course Style Guide, while contributing to the
readability of your code.
GETTING STARTED
0. Create a new Java8 project in Eclipse. You can name this project whatever you like, but
Generating Philosophy is a descriptive choice. Then create a new class named Main with a public
static void main(String[] args) method stub.
EVEN NUMBER GENERATOR
1. Create an new class named EvenNumberGenerator that implements both Iterable<Integer and
Iterator<Integer. The signature of the constructor for this class should match the following, and
the behavior of the methods that must be defined in this class are also described in these
comments:
Implement this constructor along with each of the required methods associated with the
interfaces implemented by this class: hasNext(), next(), and iterator(). Note that although it is
common to separate the functionality of Iterator and Iterable into separate classes, we can
make our Iterator EvenNumberGenerator Iterable by having it return a reference to itself from
its iterator() method.
2. From the main method of your Main class, instantiate and test and instance of your
EvenNumberGenerator class. You should test it both by calling it’s methods directly, and by
using it within a for-each loop. For example, one such test might include the following code
which prints out: 12 14 16 18 20
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/**
* Initializes a new EvenNumberGenerator to return a single even number
* each time it's next() method is called. The first even number returned
* in this way is firstEven. Subsequent even numbers returned in this way
* will be the smallest even number that is larger than the previous.
* <p
* After numberOfEvens numbers have been generated and returned from this
* next() method, the generator will end: its hasNext() method will return
* false, and its next() method will throw a NoSuchElementException when
* called after this point.
*
* @param numberOfEvens - the number of evens that can be generated
* @param firstEven - the first and smallest even that will be generated
* @throws IllegalArgumentException - when numberOfEvens is negative, or
* when firstEven is not an even number
*/
public EvenNumberGenerator(int numberOfEvens, Integer firstEven) throws IllegalArgumentExce
// TODO : implement this constructor
}
NUMBER GENERATOR
3. Since generating sequences of even numbers may be of limited use, we’ll next create a more
general NumberGenerator class. By copy+pasting the EvenNumberGenerator class within the
“Project Explorer” in Eclipse, you can give this copy the new class name NumberGenerator, and
maintain a copy of the code from your previous class to start working from.
4. The part of this class that we’d like to generalize is the part of the next() method that adds two to
the previous even number, to compute the smallest even number that is larger than the last.
Instead of only adding two, we’d like each NumberGenerator object to be able to perform an
arbitrary computation to calculate the next number, based on the previous. We’ll use the
Function<T,R interface from the JavaAPI to store and make use of this arbitrary computation
within an object. Notice that implementing this interface requires a single method definition,
and that this method will determine how we calculate the next number that we generate based on
the previous one:
Add a third parameter to your NumberGenerator constructor that has the type
Function<Integer,Integer, and then store the value passed into this constructor within a private
instance field. Instead of adding two to your previous even number to compute the next, you’ll
compute the next by calling this apply method. The input to this method is your previous
number, and the return value will be the next. While updating your NumberGenerator class, you
should also remove the restriction of only allowing an even starting value from the constructor.
5. To test and make use of your NumberGenerator class, you’ll want to define some classes that
implement the Function<Integer,Integer interface. To do this, let’s define a class called
DoubleFunction which implements the Function<Integer,Integer interface in our Main.java
source file (remember that we must leave off the public access modifier when defining a class in a
file with a different name). The apply method in this class should return a value that is double or
two times the input. With this implementation, the following code should print out: 2 4 8 16 32
GENERATOR
6. Let’s further generalize our NumberGenerator class by creating a copy of that class named
Generator (use Eclipse’s copy+paste tool again, like we did in step 3). The generalization that
we’d like to implement is to make this new Generator class work with any type of object, instead
of only working with Integer objects. We’ll accomplish this by making use of a Generic class
parameter.
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for(int i : new EvenNumberGenerator(5, 12))
System.out.print(i + " ");
1 public R apply(T t);
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for(int i : new NumberGenerator(5, 2, new DoubleFunction()))
System.out.print(i + " ");
7. To test this Generator class, let’s create an AddExclamationFunction class that implements the
Function<String,String interface. We’ll once again include this class definition within
Main.java (since it is such a simple class). The apply method in this class should return the input
string with one extra exclamation mark appended to the end. The following is one test that you
can run using these new classes (Generator and AddExclamationFunction), which should result
in displaying: Hello Hello! Hello!! Hello!!!
PHILOSOPHY
8. Now that we have developed a general Generator class, let’s make use of that Generator to
implement one more application. An interesting observation was made several years back, that
the following process will lead you to the Wikipedia page for Philosophy, when followed from as
many as 97% or random starting Wikipedia pages. 1) Choose a random starting Wikipedia page,
2) follow the first link within this page’s description text (excluding pronunciation and citation
links), and then 3) repeat step 2 until the page for Philosophy has been reached. Here’s a short
video about this observation: https://www.youtube.com/watch?v=Q2DdmEBXTpo
9. We could view this process of following Wikipedia links from one page to the next as a
Generator. In fact we can use our Generator to implement this, if we first define an appropriate
implementation of the Function interface. Here is the code for such a class (put this code in it’s
own source file) that utilizes the jsoup library, you can download the .jar file here.
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for(String i : new Generator<String(4, "Hello", new AddExclamationFunction()))
System.out.print(i + " ");
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import java.io.IOException;
import java.util.function.Function;
import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.select.Elements;
public class NextWikiLinkFunction implements Function<String,String {
@Override
public String apply(String t) {
try {
// Download a Wikipedia page, using t in their internal link format: /wiki/Some
Document doc = Jsoup.connect("https://en.wikipedia.org" + t).get();
// Use .css selector to retrieve a collection of links from this page's descrip
// "p a" selects links within paragraphs
// ":not(span a)" skips pronunciations
// ":not(sup a)" skips citations
Elements links = doc.select("p a:not(span a):not(sup a)");
// return the link attribute from the first element of this list
return links.get(0).attr("href");
// Otherwise return an appropriate error message:
} catch(IOException|IllegalArgumentException e) {
return "FAILED to find wikipedia page: " + t;
} catch(IndexOutOfBoundsException e) {
return "FAILED to find a link in wikipedia page: " + t;
}
}
}
10. Your last job for this assignment is to make use of the provided NextWikiLinkFunction with your
Generator class. Remove any previous tests from the main() method within your class Main, and
replace them with the following. Implement a console based interface that prompts the user to
enter the name of a potential Wikipedia page. Based this this starting page, your code should
generate a maximum of 100 Wikipedia page links by repeatedly following the first link within
each pages description (using the provided NextWikiLinkFunction class). After reaching the link
to the page /wiki/Philosophy, or retrieving either of the error links (that start with “FAILED “)
your program should stop. All of the links up to this point should be displayed in a numbered list
by your program. Two last implementation details to be aware of: there are no spaces in any of
these Wikipedia links, and that they all start with “/wiki/”. If the user enters spaces, you should
convert those spaces into underscores for them. You should also prepend “/wiki/” in front of the
user’s input before passing it into a new Generator. Here are two sample logs that demonstrate
using this complete application (the user’s input is displayed in a bold orange font):
Please enter a Wikipedia topic: american english
0: /wiki/american_english
1: /wiki/Language_variety
2: /wiki/Sociolinguistics
3: /wiki/Society
4: /wiki/Social_group
5: /wiki/Social_science
6: /wiki/Discipline_(academia)
7: /wiki/Knowledge
8: /wiki/Fact
9: /wiki/Verificationism
10: /wiki/Philosophy
Please enter a Wikipedia topic: this does not exist
0: /wiki/this_does_not_exist
1: FAILED to find wikipedia page: /wiki/this_does_not_exist
11. Congratulations on finishing this CS300 assignment! After verifying that your work is
correct, and written clearly in a style that is consistent with the course style guide, you
should submit your work through zybooks. The most recent of your highest scoring
submissions prior to the deadline of 17:00 on Thursday, November 2nd will be
used as part of your score for this assignment. Additional grading tests will then be
run against your highest scoring submission, and human graders will also review the
commenting, style, and clarity of this code to determine the rest of your assignment
grade.