Event loopsProgramming in prehistoric timesVery early interactive programsCommand-driven programs (20 years ago)Modern event-driven programsJava hides the event loopBuilding a GUIThe EndEvent loopsProgramming in prehistoric times•Earliest programs were all "batch" processing•There was no interaction with the userInputOutputProcessVery early interactive programs•BASIC was an early interactive language•Still a central computer, with terminals•Style of interaction was "filling out forms"Process inputAsk user for inputAsk user for inputProcess inputetc.Command-driven programs(20 years ago)•Allowing the user to enter "commands" was more flexible•Still only a single source of inputs•Not good enough for modern programsAsk user for commandRead and parsecommandExecute commandquitModern event-driven programs•Multiple sources of input–mouse clicks–keyboard–timers–external events•Requires a new program structureWait for eventDispatch eventQuitJava hides the event loop•The event loop is built into Java GUIs–GUI stands for Graphical User Interface•Interacting with a GUI component (such as a button) causes an event to occur•An Event is an object•You create Listeners for interesting events•The Listener gets the Event as a parameterBuilding a GUI•To build a GUI in Java,–Put some Components in a window–Add Listeners, usually one per Component–Put code in the Listeners to do whatever it is you want done•That's it!–Of course, there are a lot of details....The
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