Adding a an element to a vector

[Doit]

The add method of vector class returns false if you attempt to add an element with a duplicate value.
But i believe vectors allow duplicate values. Am i missing something here?
- Thanks

[Paul A]

Vector provides the add() method because it implements the List interface. Now, the point to understand here is, the behaviour of this method is dependent on the class that implements this interface (here, Vector). As List (which is acutally a Collection) is an interface, the contract that it defines for add() method is quite loose. Different implementations may ( and should ) provide different behaviour. For. eg. the add() method of a class implementing Set should return false if you try to add a duplicate element.
But Vector being a List, can support duplicate elements and so it always returns true.
HTH,
Paul.
http://pages.about.com/jqplus
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[Paul A]

So the statement that you wrote "The add method of vector class returns false if you attempt to add an element with a duplicate value." is not correct. It always returns true.
It is correct for a class implementing Set though.