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Framework for Interactive Applications
Matthew Korchinsky
Advisor: Aaron Cass
Senior Project – Computer Engineering – 2006
Abstract
The Java language was written to accomplish many different tasks therefore it is made up of a large number of classes. Although Java is
extremely versatile it can be cumbersome to use when one is designing an interactive application, especially for beginners. One negative
aspect is the complex listening system Java uses to service events. When one is learning event programming the listening system can be
complex and difficult to learn. Another is the large amount of possible classes to use to create an effective Graphical User Interface. Although
this allows for many different designs it could overwhelm the programmer. This project seeks to aid both of these problems by creating a new
event system and a tailored set of classes that can be used in a wide variety of interactive applications.
Inspiration and Background
The idea for the new event system comes from a framework called QT which is used for C++ (www.trolltech.com).
This system uses a “Signal – Slot” relationship instead of listeners to respond to events. When the programmer is
creating their application, signals are simply “connected” to slots. At runtime, when the signals are emitted in the
program, the appropriate slot is retrieved and invoked. QT uses a automatic code generation script for the code to
invoke methods, however this piece of the event system was improved upon in the Java version.
Connect, Emission of Signals, and Reflection
Connections and Data Structures
To connect a signal to a slot the user must specify the source of the
event, the signal name, the object where the slot is defined, and the
slot name. The user can also define their own signals and emit them
at the appropriate time using the emit method. They can specify the
source, signal name, and the required parameters when calling the
emit method. To alleviate the problem of an automatic code
generation script Java Reflection was used to invoke the slots when
the signals were emitted.
The connections are managed using a Java HashMap data
structure. In each connection there are four objects that must
be stored, however a HashMap can only relate two objects.
The source and signal had to be packaged together using a
new data structure (SourceSignalPair) and the destination and
slot were also packaged together (DestSlotPair). This allowed
the HashMap to be used to relate a SourceSignalPair to a
DestSlotPair.
Evaluation
The source code was given to three students. All three students had varying levels of Java knowledge ranging from intermediate event
programming experience to expert event programming experience. The students were asked to write a simple application with two buttons that
printed out different statements based on what button was pressed. They had to perform this task using the new framework and the old Java
listening system. The new event system received mixed reviews and the students stated their previous knowledge of Java listeners as the
reason.
Future Work
More time can be devoted to creating a tailored set of classes that can be used across a wide variety of interactive applications. Also a new
evaluation would be helpful among event programming beginners to determine whether the goal of the framework has been truly achieved.