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Caret events occur when the caret the cursor indicating the insertion point in a text component moves or when the selection in a text component changes. The text component's document can initiate caret events when it inserts or removes text, for example.[PENDING: Image showing sample caret forthcoming.]
You can attach a caret listener to an instance of anyJTextComponent
subclass with theaddCaretListener
method.
Note: An alternate way of detecting caret changes is to attach a listener directly to the caret object itself rather than to the text component that manages the caret. A caret fires change events (not caret events), so you would need to write a change listener rather than a caret listener.Here is the caret event handling code from an application called
TextComponentDemo
:... //where initialization occurs CaretListenerLabel caretListenerLabel = new CaretListenerLabel("Caret Status"); ... textPane.addCaretListener(caretListenerLabel); ... protected class CaretListenerLabel extends JLabel implements CaretListener { ... //Might not be invoked from the event dispatching thread. public void caretUpdate(CaretEvent e) { displaySelectionInfo(e.getDot(), e.getMark()); } //This method can be invoked from any thread. It //invokes the setText and modelToView methods, which //must run in the event dispatching thread. We use //invokeLater to schedule the code for execution //in the event dispatching thread. protected void displaySelectionInfo(final int dot, final int mark) { SwingUtilities.invokeLater(new Runnable() { public void run() { if (dot == mark) { // no selection ... } }); } } }You can find a link to the source file for
Note: ThecaretUpdate
method is not guaranteed to be called in the event-dispatching thread. To use any methods inside ofcaretUpdate
that update the GUI special handling is required to ensure they are executed on the event-dispatching thread. You can do this by wrapping the code inside aRunnable
and callingSwingUtilities.invokeLater
on thatRunnable
.TextComponentDemo
in the example index for Using Swing Components. For a discussion about the caret listener aspect of the program see Listening for Caret and Selection Changes in Text Component Features.
Because
CaretListener
has only one method, it has no corresponding adapter class.
Method Purpose caretUpdate(CaretEvent)
Called when the caret in the listened-to component moves or when the selection in the listened-to component changes.
Method Purpose int getDot()
Returns the current location of the caret. If text is selected, the caret marks one end of the selection. int getMark()
Returns the other end of the selection. If nothing is selected, the value returned by this method is equal to the value returned by getDot
. Note that the dot is not guaranteed to be less than the mark.Object getSource()
(injava.util.EventObject
)Returns the object that fired the event.
The following table lists the examples that use caret listeners.
Example Where Described Notes TextComponentDemo
Listening for Caret and Selection Changes Uses a listener label to display caret and selection status.
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