2. Outline
I. What is an event driven system?
II. What is event driven programming?
III. Course Overview
3. I. What is an event driven system?
• An event is an occurrence of interest
– Events take place at a particular time
• An event driven system is a computer
system where events are a driving force
– Events from the user (mouse click)
– Internal events (variable assignment, timers)
– Events from other computing systems (any
message arriving across the network)
4. Examples of Event Driven Systems
• Vending Machines
• Cruise Control System in a car
• TV
• Any modern windowing program
– e.g. PowerPoint
What are the events associated with each of
these?
5. II. Event Driven Programming
• Fundamentally a different paradigm from
procedural (or OOP or functional or logic)
programming
– System is made of objects
– System spends much of its time in stasis
– Events occur that propagate through the
system and then it returns to statis
6. Basic Event Driven Programming
Model
Event Source Event Handler
System Objects
notifies
modifies
7. What makes this model unique?
1. Loose Coupling between source and
handler
– Runtime registration
– Multicasting
– Multiplexing
– Separate Compilation
– Inverted Semantics
8. Differences continued
2. State based control
• Behavior of system depends on its state
• E.g. Coke machine only delivers pop after
enough money has been inserted
• Good ways and bad ways to implement this
9. Differences continued
3. Concurrent and Distributed processing
• If a handler takes too much time, other
events might be delayed/lost
• One solution is to have handler execute is a
separate thread.
• Concurrency concerns now become important.
• E.g. what happens is multiple events arrive in
rapid sequence? Might there be multiple threads
executing in the same handler?
10. Concurrent and Distributed
Processing - continued
• Distributed Processing
– Source and Handler might be on different
computing systems entirely.
– E.g. a web browser makes a request for a
web page from a server.
– Client / Server computing is fairly well
understood. There are many other models,
however.
11. Course Outline
• Java Event Driven Programming
• Component Based Programming in Java
• Concurrent and Distributed Event
Programming
• Software Engineering Event Driven
Systems
