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The JHAVÉ Project
• JHAVÉ: Java Hosted Algorithm Visualization Environment
• Goal: Development of a comprehensive suite of visualization-based
materials for teaching algorithms and data structures, work was
partially supported by a National Science Foundation Grant, CCLIEMD #0126494
• Principal Investigators:
• Scott Grissom (Grand Valley State University)
• Myles McNally (Alma College)
• Thomas Naps (University of Wisconsin - Oshkosh)
•
Website: http://jhave.org
JHAVÉ “supports” Effective AV -- How?
• “Stop-and-think” questions
• Documentation window
• Pseudo-code window
• Input generators
• Audio accompaniment
A Tour of the JHAVÉ Website
JHAVÉ Organization
• Client-server mode of operation
• Generation of visualization script occurs by running
algorithm on server
• Viewing of script handled by “dumb” rendering
client
• Webstart facilitates deployment
• Users just need to access the appropriate website
to run the client on their machine
• JHAVÉ supports a variety of scripting languages
through plug-ins
The JHAVÉ Client-Server Model
Algorithm Choice
Input Generator
Presented
Choice
Input
Generator
Input
Script is Rendered
Vis
Script
Client
Data Flows
Appropriate Input
Generator Served
Appropriate Script
Generation
Program Run
Server
Overall GAIGS VIS Script Structure
• A GAIGS visualization script is defined in a show file
• The general script structure is:
• one or more snapshots
• followed by an optional question collection
• The show file could be created by hand, or (more
usually) as the output of a script generating program
Example of Overall Script Structure
<show>
<snap> … </snap>
<snap> … </snap>
<snap> … </snap>
<questions> … </questions>
</show>
A Show File with Three Snapshots and a Question Collection
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE show PUBLIC "-//JHAVE//DTD GAIGS SHO//EN" "gaigs_sho.dtd">
A Simple, but Complete, Example
<show>
<snap>
<title>queue</title>
<pseudocode_url>index.php?line=2</pseudocode_url>
<queue>
<list_item color="#0000FF">
<label>9</label>
</list_item>
</queue>
<question_ref ref="0"/>
</snap>
<questions>
<question type="MCQUESTION" id="0">
<question_text>Color of the next queue item?</question_text>
<answer_option>red</answer_option>
<answer_option is_correct="yes">green</answer_option>
<answer_option>blue</answer_option>
</question>
</questions>
</show>
A Simple Visualization Script with a Multiple Choice Question
Generating Scripts
• GAIGS XML scripts can be generated by programs
written in any programming language
• However, the JHAVÉ environment is designed to
directly support programs written in Java
• Input to programs must be specified on the
command line
• The first command line parameter is the file name
the script is to be written to
• Support classes are available which can be used to
directly generate the required GAIGS XML
Support Classes for Script Generation
• ShowFile: Handles the actual writing to the script file
• Structure Classes: Basically one for each of the
GAIGS built-in structures
• Linear Structures: GAIGSstack, GAIGSqueue,
GAIGSlist
• Arrays: GAIGSarray (includes bar graphs)
• Trees and Graphs: GAIGStree, GAIGSgraph
• Text: GAIGStext
• Question Classes: Support various aspects of
generating questions in scripts
• XMLfibQuestion, XMLmcQuestion,
XMLmsQuestion, XMLtfQuestion
The ShowFile Class
• The ShowFile class is responsible for all writing to the
script file
• Constructors:
• ShowFile(String fileName)
• file is opened, and preliminary XML written to it
• Key Methods:
• writeSnap(String title, Double titleSize,
GAIGSdatastr… ds)
• writes to the file the XML for a snap with the title
and each of the listed structures
• close()
• writes any questions and closes the file
The GAIGSstack Class I
• GAIGSstack functions in the usual way as a stack (with
push and pop operations
• But also stores color and other information in a way that
can remain hidden (if desired) from the client class
• Constructors:
• GAIGSstack()
• create a stack using defaults for location and color
• GAIGSstack(String n, String c, double x1, y1, x2, y2,
size)
• create a stack with name n, color c, location
<(x1,y1),(y2,y2)>, and fontSize size
The GAIGSstack Class II
• Key Methods:
• pop()
• push(Object o)
• push(Object o, String c)
• Key Inherited Methods (from GAIGSlist)
• isEmpty()
• peek()
import exe.*;
import java.io.*;
public class Example1 {
static final String title = "Stack Example";
static final double titleSize = 0.08;
public static void main (String [] args) throws IOException {
GAIGSstack stack = new GAIGSstack();
ShowFile show = new ShowFile(args[0]);
int itemsToAdd = Integer.parseInt(args[1]);
for (int i = 0; i < itemsToAdd; i++) {
stack.push(i);
show.writeSnap(title, titleSize, stack);
}
show.close();
}
}
Example Code: Using the ShowFile and GAIGSstack Classes
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE show PUBLIC "-//JHAVE//DTD GAIGS SHO//EN"
"gaigs_sho.dtd">
ShowFile constructor
<show>
<snap>
<title>Stack Example</title>
<stack>
<bounds x1="0.0" y1="0.0" x2="1.0" y2="1.0" fontsize="0.05"/>
<list_item color="#FFFFFF">
<label>0</label>
</list_item>
ShowFile writeSnap
</stack>
</snap>
<questions>
</questions>
</show>
ShowFile close
Example Output: itemsToAdd == 1
GAIGSarray I
• GAIGS provides support for one and two dimensional
arrays
• Row labels can be specified, and if the array is 2-d
column labels as well
• If the array is a 1-d array of int, it can be shown either
in the usual format or as a bar graph
• Here we just briefly consider the 1-d case, please
consult the GAIGS API for complete details on this
class
GAIGSarray II
• Constructor:
• GAIGSarray (String s, boolean bar, color c, double
x1, y1, x2, y2, size)
• create a label with name s, color c, location
<(x1,y1),(y2,y2)>, and fontSize size. Display as
a bargraph if bar == true
GAIGSarray III
• Key Methods:
• set(Object o, int loc) and set(Object o, int loc,
String c)
• set location loc to have value o, optionally with
color c
• get(int loc)
• return the value at location loc
• setColor(int loc, String c)
• set the color of the item at location loc to c
• setName(String s)
• set the name of this structure to s
Activity: Bubblesort Visualization
• Our exercise will be to create a complete visualization
for the (infamous) Bubblesort algorithm
• Supplied code will create the snapshot shown below:
Supplied Code
import java.io.*;
import java.util.Random;
import exe.*;
public class Sort {
static final String TITLE = null;
static int arraySize;
static GAIGSarray items;
// no title
// # of items to sort
// the array of items
Exercise Code: Preamble
public static void main(String args[]) throws IOException {
// process program parameters and create the show file object
ShowFile show = new ShowFile(args[0]);
arraySize = Integer.parseInt(args[1]);
// define the two structures in the show snapshots
items = new GAIGSarray(arraySize, true, "BubbleSort",
"#999999", 0.1, 0.1, 0.9, 0.9, 0.07);
// initialize the array to be sorted & show it
loadArray();
show.writeSnap(TITLE, items);
for (int pass = 1; pass < arraySize; pass++)
for (int i = 0; i < arraySize-pass; i++)
if ((Integer)(items.get(i)) > (Integer)(items.get(i+1)))
swap(i, i+1);
// visualization is done
show.close();
}
Exercise Code: Main method
// Load the array with values from 1 to the array size, then
// shuffle these values so that they appear in random order.
private static void loadArray () {
Random rand = new Random();
for (int i = 0; i < arraySize; i++)
items.set(i+1,i);
for (int i = 0; i < arraySize-1; i++)
swap(i, i + (Math.abs(rand.nextInt())
% (arraySize - i)) );
}
// Swap two items in the array.
private static void swap (int loc1, int loc2) {
Object temp = items.get(loc1);
items.set(items.get(loc2), loc1);
items.set(temp, loc2);
}
Exercise Code: Support Routines
If you decide to do the activity …
1. Decide when snapshots should be taken (when do
the interesting events occur?)
2. Use coloring to show the ongoing actions of the
algorithm
3. Use the name of the array to produce useful
messages about the status of the algorithm
Adding Interactive Questions
• GAIGS Scripts can be used to ask four types of
questions:
• True / False
• Fill in the Blank
• Multiple Choice
• Multiple Selection
A Multiple Choice Question
Question Basics
• All the questions in a GAIGS script are collected at
the end of the XML File
• Each contains a unique ID number/identifier
• A snapshot can contain a question reference
• The reference is by ID number/identifier
• A question reference causes the question to
appear when the snapshot is shown
Question Generation Support I
• As for GAIGS structures, there are support classes for
the generation of question XML
•
•
•
•
XMLtfQuestion:
XMLmcQuestion:
XMLmsQuestion:
XMLfibQuestion:
true / false
multiple choice
multiple selection
fill in the blank
• Each support class allows the definition of the
question text, choices, and correct answer(s)
Question Generation Support II
• To include a question in a snap, pass a question in
ShowFile method writeSnap
• This method also require documentation and
pseudocode urls (which may be null)
• writeSnap(String title, double titleSize, String doc_url,
String pseudo_url, question q, GAIGSdatastr… ds)
• writes to the file the XML for a snap with the title,
titleSize, documentation and pseudocode urls, a
question and each of the listed data structures
XMLtfQuestion
• Constructor:
• XMLtfQuestion(ShowFile f, String id)
• The id string must be unique within a script
• ShowFile reference is a legacy code issue
• Key Methods:
• setQuestionText(String text)
• sets the text which will be displayed as the
question
• setAnswer(boolean value)
• set the correct answer to value
XMLtfQuestion Example
int id = 0;
boolean swapIsDone = false;
…
XMLtfQuestion tf = new XMLtfQuestion(show, id + "");
id++;
tf.setQuestionText("Will a swap be done next?");
…
show.writeSnap(TITLE, null, null, tf, …);
…
tf.setAnswer(swapIsDone);
XMLfibQuestion
• Constructor:
• XMLfibQuestion(ShowFile f, String id)
• The id string must be unique within a script
• ShowFile reference is a legacy code issue
• Key Methods:
• setQuestionText(String text)
• sets the text which will be displayed as the
question
• setAnswer(String text)
• set text to be one of answers to be accepted as
correct
XMLfibQuestion Example
int id = 0;
int swapsThisPass = 0;
…
XMLfibQuestion fib = new XMLfibQuestion(show, id + "");
id++;
fib.setQuestionText("How many swaps will be made this pass?");
…
show.writeSnap(TITLE, null, null, fib, …);
…
fib.setAnswer(swapsThisPass + "");
Probabilistic Question Asking
• The support classes allow the user to define the
number of questions to be asked during a session,
despite how many are “added”
• To do this, use the alternative constructor for
ShowFile:
• ShowFile(String fileName, int count)
• Exactly count questions will be asked (as long as at
least that many questions have been added)
Next Activity: Bubblesort + Questions
Return to your Bubblesort visualization and
1. Add a question which asks how many swaps will be
made during the next pass (asked just before a pass)
2. Add a question which asks if a swap will be made
(asked just before a comparison is made)
3. Use probabilistic questioning to limit the number of
questions asked during a session