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UnsuppourtedOperationException when tried to modify the Collections.unmodifiable format .

PavanPL KalyanK
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Joined: Feb 28, 2009
Posts: 212


I read that we would get an UnsuppourtedOperationException when tried to modify the Collections.unmodifiable format .

But why i am not getting any exception .The console is blank
Henry Wong
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Joined: Sep 28, 2004
Posts: 18896
    
  40

But why i am not getting any exception .The console is blank


The Collections.unmodifiableList() method returns a read-only list. It doesn't change the list that is passed to it.

Henry


Books: Java Threads, 3rd Edition, Jini in a Nutshell, and Java Gems (contributor)
PavanPL KalyanK
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Joined: Feb 28, 2009
Posts: 212
I tried as you said .and i got my Exception

Exception in thread "main" java.lang.UnsupportedOperationException
at java.util.Collections$UnmodifiableCollection.add(Unknown Source)
at Tes.main(Tes.java:19)


Thank you.
Campbell Ritchie
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Joined: Oct 13, 2005
Posts: 39436
    
  28
You need to read the documentation for List#add() which explains it. Also the Collections#unmodifiableList(java.util.List) method.

The return value is specifically designed not to allow additions or removals from the List. So it throws Exceptions if you try to use the unimplemented methods.
If the original List changes, the "unmodifiable" copy changes to match, however.
 
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