Problem
In oracle j developer 9i the structure window is not being show, when it is clicked from view
--> structure window, some weird error is coming :
java.lang.NullPointerException at oracle.ideimpl.explorer
Solution
· You can try to wipe out any ".layout" files that you have in your JDeveloper system directory. These can be found in <JDEV_HOME>/jdev/system or <JDEV_HOME>/jdev/system9.0.X .X.X depending on which version of JDeveloper you are running.
Wiping out a .layout file is harmless. It contains only a record of which windows were opened, and what locations they were opened at. Wiping them out simply causes JDeveloper to default to its out of the box settings. So, if you repositioned (i.e. "docked") any windows for a particular layout, you will lose those settings
Solution worked for me
Editing .layout is removed from <JDEV_BIN>/jdev/system9.0.X .X.X and it is working fine for me.