3/2/09
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6.1 – GUI Elements
! Command-line applications,
interact with the user through simple prompts and feedback
! … but they lack the rich user experience
! With GUI, the user is not limited to responding to prompts in a
particular order and receiving feedback in one place
! Three kinds of objects are needed to create a GUI in Java
components
events
listeners
6.1 – Components, Events, Listeners
! Component –defines a screen element used to display information
or allow the user to interact with the program
A container is a special type of component that is used to hold and
organize other components
! Event – an object that represents some occurrence in which we may
be interested
Often correspond to user actions (mouse button press, key press)
Most GUI components generate events to indicate a user action related
to that component
Program that is oriented around GUI, responding to user events is called
event-driver
! Listener – an object that “waits” for an event to occur
and responds in way when it does
In designing a GUI-based program
we need to establish the relationships between the listener,
the event it listens for, and
the component that generates the event
6.1 – GUI Elements
! To create a Java program that uses a GUI, we must:
instantiate and set up the necessary components,
implement listener classes that define what happens when
particular events occur, and
establish the relationship between the listeners and the
components that generate the events of interest
! Java components and other GUI-related classes are
defined primarily in two packages
java.awt
javax.swing
6.2 – Components
! A variety of interactive components
Buttons – of course…
text fields –input from keyboard
check boxes – a button that can be
toggled on or off using the mouse
(indicates a boolean value is set or
unset)
radio buttons –to provide
a set of mutually exclusive options
sliders – specify a numeric value
within a bounded range
combo boxes – select one of several
options from a “drop down” menu
