JAVA错误：Exception in thread "main" java.lang.NullPointerException

JAVA error: Exception in thread "main" java.lang.NullPointerException
example:

Exception in thread "main" java.lang.NullPointerException
at javax.swing.ImageIcon.<init>(Unknown Source)
at chuangti.Example1.CreateJFrame(Example1.java:41)
at chuangti.Example1.main(Example1.java:84)

answer　

i.e. java.lang.NullPointerException // pointer to null 
at javax.swing.ImageIcon. <init> (Unknown Source) // empty area 
at chuangti.Example1.CreateJFrame (Example1.java:41) // 41 lines 
at chuangti.Example1.main (Example1.java:84) // 84 lines