same problem in the iMac.
the default Java Machine is /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home/

java.lang.NullPointerException
at users.sgeducation.lookang.DCmotor10_pkg.DCmotor10View.reset(DCmotor10View.java:3835)
at org.colos.ejs.library.Animation.reset(Unknown Source)
at users.sgeducation.lookang.DCmotor10_pkg.DCmotor10Simulation.(DCmotor10Simulation.java:23)
at users.sgeducation.lookang.DCmotor10_pkg.DCmotor10.(DCmotor10.java:147)
at users.sgeducation.lookang.DCmotor10_pkg.DCmotor10Applet.init(DCmotor10Applet.java:25)
at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Plugin2Manager.java:1640)
at java.lang.Thread.run(Thread.java:680)

it works well in windows.