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Problem in Generics Wildcard characters

 
Ranch Hand
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Hi

I have a question in generics regarding the wilcard characters.Wilcard characters when used during the creation of instance behave strange.

consider the following statement.

List<?> list = new ArrayList<?>();

Above statement gives me compile time error.

List<List><?>> lists = new ArrayList<List><?>>();

Above statement is working fine.My Question is why?

what is the problem with the first one?


Any help would be appreciated.

 
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Posts: 2700
IntelliJ IDE Opera
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Because the ? can only be used in a reference context.
In your first code block you're trying to use it as a type.
The left side of the = is fine.

The second block compiles because there you're using the question mark in a reference context.


Don't really know how to explain this but I hope this helps.
 
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