---- 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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