focus : Java Glossary

Tips

• Component.requestFocus won’t work until after the frame is completely painted. This means you must usually put such code inside a WindowListener.
• Like all Swing and AWT (Advanced Windowing Toolkit) calls, requestFocus calls should run the EDT (Event Dispatch Thread) thread.
• Component.transferFocus lets you hand focus off to some other component.
• Component.hasFocus lets you determine if a given Component has focus.
• KeyboardFocusManager.getFocusOwner lets you ask which Component currently has focus.
• Call getFocusOwner on all windows in your application. (Frame.getFrames() followed by calling getOwnedWindows on each of them recursively should get you a full list).
• Java version 1.4 now handles focus and traversal with in totally new way with FocusTraversalPolicy.
• JSpinners will drive you little crazy in FocusTraversalPolicy.getComponentAfter because you don’t get passed the address of the JSpinner, but rather an associated JFormattedTextField that helps implement it. I consider this a bug. You have to use Jspinner.getEditor.getComponent(0) in FocusTraversalPolicy.getComponentAfter method.
• Prior to 1.4 there were over a hundred outstanding bugs in focus handling. You had to use isManagingFocus( false ).
• I hope this is too obvious to mention, but when you have a modal dialog up, no other window can have focus.

Sample Code

Enabing Tab and Shift-Tab

Focus Box

theButton.setFocusPainted( false );

Learning More