Java 1'1 Event Model

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Java 1.1 Event Model

• An Examination of the Event Delegation Model

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What Well Cover

• Javas original event model
• The four concepts of the Java 1.1 event model
• Event Classes
• Event Listeners
• Explicit Event Enabling
• Adapters

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Original Event Model

• Outward rippling model
• Events only visible to original container, or its
  containers
• Lots of waste - no way to disable uninteresting
  events
• 1.1 Model - event delegation

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1.1 Model - Event Classes

• Event classes - classes for objects generated by
  the UI events
• All inherit from java.util.EventObject
• Via the java.awt.AWTEvent
• All the remaining classes of the event-delagation
  model are in the java.awt.event package.

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1.1 Model - Event Listeners

• Event listeners - classes that implement an event
  listener interface for a particular type of event
• The event listeners are then added to the list of
  event listeners for the object generating the
  event

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Explicit Event Enabling

• Alternative to delegation, explicit enabling
• UI components call enableEvents() and have a
  method to process them
• The super.processXXXEvent() must be called
• This will process events prior to any event
  listeners

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1.1 Model - Adapters

• Several of the listener interfaces have multiple
  methods.
• Since it can be inconvenient to implement all the
  methods if you only need one, Java has adapters
• Adapters implement all methods of an interface
  with methods that do nothing.

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What we covered

• The limitations of Javas original event model
• Event Classes
• Event Listeners
• Explicit Event Enabling
• Adapters