YARI is a comprehensive tool suite to debug (layouts), spy, spider, inspect and navigate SWT and Eclipse based application GUIs (Workbench or RCP) at runtime.
Swing Spy is java based Swing/AWT spy agent that prints the widget under the cursor (like Spy++ for Windows/MFC and SWT Spy for Java-SWT). Download from the homepage: http://www.nenoff.com/swingspy/