UnsuppourtedOperationException when tried to modify the Collections.unmodifiable format .

[PavanPL KalyanK]

try
	{
ArrayList al = new ArrayList();
al.add("arg0");
Collections.unmodifiableList(al);
al.add("two");
	}
	catch(Exception e)
	{
	System.out.println(e.getMessage());	
	}

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]

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

[PavanPL KalyanK]

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]

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.