Optimization of java.awt.Component's initialization
Author: Dafe Simonek
$Revision: 1.2 $
$Date: 2003/02/07 19:30:48 $
Document history: available in
CVS
What is this technique good for
Use following technique when init of your component takes noticeable amount of
time so that it slows down init of some dialog or frame significantly.
Main trick is to defer expensive parts of initialization to later time. Later
time here is defined as the time right after first paint, when paint event
arrives. Majority of the init time is often spent in filling the component with
data or widgets that are not likely to be used in first seconds of use anyway,
so we can safely load and draw them later, not in first paint.
Things like explaining descriptions, long lists in combo boxes, large background
images are good candidates for their later loading.
Implementation steps:
1. Identify expensive parts of code which could be loaded later, after first
paint.
Use profiling techniques
article tips to profile dialog ir frame initialization code.
2. Implement
org.openide.util.AsyncGUIJob interface.
Convenient way is to add implementation of AsyncGUIJob
right into code of component in question. See javadoc documentation of
AsyncGUIJob to find details about how and when methods in your
implementation will be called.
3. Optionally implement
org.openide.util.Cancellable interface.
Implement Cancellable interface in the case you want to allow the
system to cancel your initialization task. System will call cancel method when
component stops to be showing during its initialization phase. Cancel ability is
desirable for longer lasting init tasks like some network connections. Note that
implementation of AsyncGUIJob Cancellable interfaces
must be present in the same class to be usable for org.openide.Utilities.attachInitJob,
read below.
4. Attach init job to component using
org.openide.Utilities.attachInitJob(Component comp4Init, AsyncGUIJob
initJob).
Pass your component to be inited as first param, as second param pass implementation
of init job, optionally accompanied by Cancellable implementation.
5. Show your component as usual
Further work with component is unchanged, insert your component into AWT
hierarchy and show in dialog, wizard, frame, whatever, just like you do with
other components.
Example:
See java source
org.netbeans.core.ui.IDESettingsPanel.java for example of described technique.
UI notes:
Your component now has at two states in its visual lifecycle, "initially drawn"
and "fully drawn". Remember to not change dimensions, colors, shapes during
transition from first state to second. Goal is to make the transition as hidden
and not intrusive as it is possible.
Also, don't forget to put some "initializing" or "loading" labels on parts of UI
which init is long enough to be noticeable by user (aroung or greater then 1
second). For longer running initialization support user feedback by using busy
cursor over affected subcomponents. See article
Howto use wait and progress cursors
Please send comments to nbdev.
