How to write a Caret Listener in Java?

[Dilbert]

Hi Friends,
I not have much knowledge about the Java. Now I want to get the focus where the user will type the next character and for that I want to use Caret Listener in my coding.!! But I don't know about that. So please tell me how to write a Caret Listener in Java.?? Also please tell me the methods that are used by the caret listener, if any. Hoping that someone would help me faster.!!

[CodGuru]

You should first think about the logic for using the caret listener so that you can use easily whenever you want. The carets are the point which tell user where the next character will insert. It is same as cursor in Windows. And the caret events occurs when the text component moves. The event also takes place when the selection in a text component changes. In short, if there is change of anything that is related with caret then that event takes place.

[opaper]

I think that you should be knowing about the carets. So i though that providing you with the Interface and Class of carets would be more useful. First lets look at the CaretListener Interface. CaretListener has only one method. The following is the method for that :

1. caretUpdate(CaretEvent) - This method is called when the caret in the listened-to component moves. It is also called when the selection in the listened-to component changes.

Now lets look at the CaretEvent Class. The following are the methods used into that :

1. int getDot() - This method returns the current location of the caret.
2. int getMark() - This method returns the other end of the selection.
3. Object getSource() - This method is used when you have to return the object that fired the event.

[MELTRONICS]

You can also detect the caret changes by another way. In that method you would have to attach a listener directly to the caret object. This method is useful because there is no need to attach that to the text component that manages the caret which was described in the earlier post. The important thing you will have to note is that the caret fires change events and not the caret events. So there is absolutely no need t write a caret listener. You would need to write a change listener rather than a caret listener.

[Praetor]

I have provided you with a coding for the caret event handling from an application called TextComponentDemo :

...
CaretListenerLabel caretListenerLabel =
    new CaretListenerLabel("Status_Caret");
...
textPane.addCaretListener(caretListenerLabel);
...
protected class CaretListenerLabel extends JLabel
                                   implements CaretListener
{
    ...
    public void caretUpdate(CaretEvent e) {
        displaySelectionInfo(e.getDot(), e.getMark());
    }

    protected void displaySelectionInfo(final int dot,
                                        final int mark) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                if (dot == mark) { 
                    ...
                }
            });
        }
    }
}

[kyosang]

A caret listener must implement one method, caretUpdate. The following code is an example of CaretListenerLabel implementation of caretUpdate :

public void caretUpdate(CaretEvent e) {
    int dot = e.getDot();
    int mark = e.getMark();
    if (dot == mark) { 
        try {
            Rectangle caretCoords = textPane.modelToView(dot);
            setText("caret: text position: " + dot +
                    ", view location = [" +
                    caretCoords.x + ", " + caretCoords.y + "]" +
                    newline);
        } catch (BadLocationException ble) {
            setText("caret: text position: " + dot + newline);
        }
     } else if (dot < mark) {
        setText("selection from: " + dot + " to " + mark + newline);
     } else {
        setText("selection from: " + mark + " to " + dot + newline);
     }
}