Below is an applet for drawing a Huffman tree for a given string.
It is possible, for a variety of reasons, that the above applet might
not run on your browser. For this reason (or others), you might wish
to download the applet and run it as an application. There are two
ways to do this:
Using JavaTM
Web Start. If you have
JavaTM Web Start installed, you may simply click here to launch the program as a
stand-alone application. The application will be cached by the Web
Start, and may subsequently be started via the Application Manager.
Running the program through the Application Manager does not require
internet access; however, the Application Manager will attempt to
determine whether an update is available prior to starting the
application. On Windows, shortcuts may be added to the desktop and/or
Start menu using the Application Manager (the second time you run the
application, you will be asked whether you want this done).
Manual download. Assuming you have at
least the Java 2 runtime environment installed on your machine, you
will first need to download viewer.jar (39K -
more information on viewer.jar).
Then you will need to download huffman.jar
(21K) to
the same directory. From that directory, you may run the program by
issuing the command:
java -jar huffman.jar
On Windows, you may also run the program by double-clicking the icon
for huffman.jar.
Usage
The input consists of a string provided either as text entered in the
text field or as the contents of a specified file (the latter
option is probably prohibited by the browser if the program is
being run as an applet). Based upon this input, a Huffman tree is
generated. This tree describes a varying-length binary encoding
for each character in the input string such that the length of the
encoded string is minimized. The Huffman tree is displayed, along
with a table giving, for each character in the string, its
original encoding in hexadecimal (this helps to identify
non-printing characters), its binary Huffman code, and its number
of occurrences in the string. The Huffman code actually describes
the path from the root of the tree to the node containing the
encoded character: a 0 represents an edge to a left child, and a 1
represents an edge to a right child.
The table is initially sorted, first in nonincreasing order of number
of occurrences, then in nondecreasing order of length of Huffman
code, then in nondecreasing order of Huffman code. Using the
Sort menu, the user can choose how the table is sorted. A
stable sorting algorithm is used, so that if the table is first
sorted by one key then another, the result will have the second
key as primary key, and the first key as secondary key.
Font characteristics may be changed using the Font menu.
Error Messages
The following error messages may be displayed by the program:
Security Error Access to the file system is prohibited.
This message occurs when the runtime environment does not allow the
program access to the local file system. The most common
cause is pressing the "Choose File" button when the program
is run as an applet. Most browsers do not allow applets
access to the local file system.
Load Error Package edu.ksu.cis.viewer not found.
This message occurs when an attempt is made to draw the tree, but the
runtime system cannot find the package edu.ksu.cis.viewer.
The most probable cause is that the program is run as a
stand-alone application without Web Start (see "Manual
download" above), but the file viewer.jar has not been
downloaded to the same directory as huffman.jar.
I/O Error
This message occurs when any error occurs while the program is
interacting with the local file system; for example, the
name of a nonexistent file is given. The cause of the error
is briefly described in the message.
