Its an example of a class you'd write yourself. Although there are
similar methods on commons-collections CollectionUtils.
Stephen
Paolo Viappiani wrote:
In which package is ModelUtils?
p*
On 2/26/07, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote:
---- Vishist Mandapaka <[EMAIL PROTECTED]> wrote:
> Hi,
> Can anyone guide me with examples for Closure, Predicate, and
Transformer
> objects. I am unable to map it to any real world scenarios where these
> objects may be of use.
Closure:
========
I have a tree of Attribute objects, and for each one which has one or
more
attached errors I want to add it to a list. I therefore have a method
that
walks the tree of objects and for each node in the tree invokes a Closure
that is passed in as a parameter:
private List findErrors(AttributeGroup model) {
final List errors = new ArrayList(10);
Closure cb = new Closure() {
public void execute(Object input) {
Attribute attr = (Attribute) input;
List errList = attr.getErrorList();
if ((errList != null) && (errList.size() > 0)) {
errors.add(attr);
}
}
};
ModelUtils.forEachAttr(model, cb);
return errors;
}
The tree-walking code (ModelUtils.forEachAttr) can then be reused with
Closure objects that do other types of things.
Predicate:
Given a list of Person objects, return only those whose country attribute
has a specific value (filtering).
Transformer:
Given a list of strings, return a list of JSF SelectItem objects that
wrap
those strings, allowing the list to be displayed in a drop-down list in a
JavaServer Faces view. This same Transformer class can then be used to
generate wrappers for a list of colours, a list of countries, etc. Yes a
simple method can be written to do this, but with the Transformer
approach a
Transformer instance can then be passed around as an object without
the code
needing to know exactly *what* the Transformer will do.
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