Java Tips Weblog

It seems to me that the focus policy of JTabbedPane has changed from JDK1.4.2 to the current JDK6 version.

The current version remembers which component last had focus on a tab and will restore focus to that component again when the tab is reselected. In earlier versions the component with focus was not remembered and focus was placed on the first component on the tab each time a tab was reselected.

Both focus policies are valid. It would be nice to have control over which focus policy you want to use independent of the JDK version you are using.
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You have a text component that dislays multiple lines of text. Now you want to highlight the current line at the position of the caret. One possible way to do this might be to use a highlighter (as discussed in the last blog) and then adjust the highlight offsets whenever the caret changes location. The problem is that the default highlight painter will only highlight where text is painted. That is, the empty space to the right of the text is never highlighted. We want to highlight the entire line whether text goes to the end or not.
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All text components allow you to highlight certain portions of text. This is done by adding a highlight to the Highlighter. The highlight will then use a HighlightPainter to paint the highlight. The default painter  simply paints a coloured background. Effective but rather plain. Now is your chance to create a custom painter and jazz up the highlighting.
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Swing text components support undo/redo of text entered in a Document. Every time a change is made to the Document an UndoableEditEvent is generated. The UndoManager keeps track of these events and allows you to invoke undo/redo on them. The default implemetation of the UndoManager is to undo/redo individual events. This means each character you type is undone/redone separately. I don’t know about you, but I would rather undo/redo releated events together at the same time.

The JDK already supports a class dedicated to Text Utilities. Although you may have missed it because the class is called Utilities. The class is full of static methods to help you work with text components. Of course a few more methods would never hurt.
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There are times when you may want to monitor your application for inactivity. Maybe you want to log out a user after a certain time interval. This requirement can be broken down into two main steps. We will need to:

• listen for events at the application level
• track the time interval between these events

Whenever the time interval between events exceeds our inactivity threshhold we will then invoke the inactivity Action.

My previous entry was about using a Select All Editor in a JTable. When you double click a cell or use the F2 key to start editing a cell the editor will be displayed with the text in the cell already highlighted ready to be replaced. This is fine because the user has visual feedback that the text will be replaced if they start typing without removing the selection.

However, when you type a character when focus is still on the rendered cell the editor is invoked with the text already replaced by the character just typed. The user had no visual indication that this was going to happen.
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