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Run Time Error

Frances Hollis
Greenhorn

Joined: Sep 02, 2006
Posts: 17
OK I got my code to compile but I am getting RTE. I would appreciate if someone could give me some help. I am probably overlooking something simple because I do not have a good understanding of using the methods for Collections yet. I am still learning how to read the APIs.




Exception in thread "main" java.lang.NullPointerException
at java.util.TreeMap.compare(TreeMap.java:1093)
at java.util.TreeMap.getEntry(TreeMap.java:347)
at java.util.TreeMap.containsKey(TreeMap.java:204)
at java.util.TreeSet.contains(TreeSet.java:196)
at Roster.find(Roster.java:31)
at RosterTest.doFind(RosterTest.java:69)
at RosterTest.main(RosterTest.java:24)
Press any key to continue . . .
fred rosenberger
lowercase baba
Bartender

Joined: Oct 02, 2003
Posts: 11168
    
  16

a NullPointerExeption comes when you have a reference to an object, but no actual object has been created.

i'm guessing your trying to read something out of your Roster before you put something into it?


There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors
Prabhu Venkatachalam
Ranch Hand

Joined: Nov 16, 2005
Posts: 502



In your Student class, you are implementing compareTo method from Comparable interface. In that method, without checking whether supplied object is null or not, you are calling the method.

Try changing this like below,



Prabhu Venkatachalam<br />SCJP 1.4,SCWCD 1.4<br />prabhu.venkatachalam@gmail.com
 
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