Writing Event Listeners

How to Write a Caret Listener

Caret events occur when the caret in a text component moves or when the selection in a text component changes. You can attach a caret listener to an instance of any JTextComponent subclass with the addCaretListener method.

If your program has a custom caret, you might find it more convenient to attach a listener to the caret object rather than to the text component for which it is a caret. A caret generates change events rather than caret events, so you would need to write a change listener rather than a caret listener. See How to Write a Change Listener for information about change listeners.

Caret Event Methods

The CaretListener interface has just one method, so it has no corresponding adapter class. Here's the method:

void caretUpdate(CaretEvent)

Called when the caret in the listened-to component moves or when the selection in the listened-to component changes.

Examples of Handling Caret Events

The example described in How to Use Text Components has a caret listener that displays caret and selection status. Refer to the section titled Listening for Caret and Selection Changes for a description. You can find the source code in TextComponentDemo.java.

The CaretEvent Class

The caretUpdate method has a single parameter: a CaretEvent object. To get the text component that generated the event, use the getSource method which CaretEvent inherits from EventObject.

The CaretEvent class defines two useful methods:

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

Writing Event Listeners