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From "Jack, Paul" <>
Subject RE: [Collections][SUBMIT] TypedList
Date Tue, 23 Apr 2002 15:14:11 GMT
Hi Steve,

Your TypedList got me thinking...At first I thought, wouldn't
it be nice to specify a parameter that would allow the null 
element (sometimes I need a list that allows nulls)...then I 
got to thinking, actually wouldn't it be nice if the validate()
method could be overridden by a subclass to allow more than one
class type...then I thought, actually, wouldn't it be nice if
the validation were completely generic, so that you supplied the
validation routine in the constructor of the list...then I 
realized, the collections package already defines an interface
for validations (Predicate)... you think it's a good idea to alter TypedList so that it
takes a Predicate in its constructor?  You could then supply a
concrete Predicate that does the Class.isInstance check...


-----Original Message-----
From: Stephen Colebourne []
Sent: Sunday, April 21, 2002 2:13 PM
To: Jakarta Commons Developers List
Subject: [Collections][SUBMIT] TypedList

After a quick check, I could find no implementation of a type checking list
in collections. As I needed it, I have created one. Here is the class
 * TypedList is a list wrapper that supports type checking. Only elements
 * of the specified type (or a subclass) can be added to the list. An
 * attempt to add a different kind of object, or null, will cause an
 * <tt>IllegalArgumentException</tt>.
 * <p>
 * Constructing a new instance of this class will use an ArrayList behind
 * the scenes. Alternatively, the static <tt>wrap</tt> method can be
 * used to wrap any object implementing List.

The code is attached as a zip. Feedback welcome on whether this is suitable
for inclusion in the collections area.


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