During cold startup of java application, any touch to rt.jar will cause significant amount of time based on some experiments performance team has done.

I found that when startup MetalWorks demo on Windows platform, sun.awt.X11GraphicsEnviroment class is requested. This class is not there on Windows. So it will end up opening all the jar files on bootclasspath. The root cause is com.sun.java.swing.SwingUtilities2.isLocalDisplay just simply call Class.forName("sun.awt.X11GraphicsEnviroment") on all platforms.