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Date: Mon, 9 Oct 2006 16:23:19 -0700 (PDT)
From: "Aldrin Leal (JIRA)" <jira@apache.org>
To: commons-dev@jakarta.apache.org
Subject: [jira] Created: (LANG-283) Visitors for Builders
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Visitors for Builders
---------------------

                 Key: LANG-283
                 URL: http://issues.apache.org/jira/browse/LANG-283
             Project: Commons Lang
          Issue Type: New Feature
    Affects Versions: 2.2
         Environment: Any
            Reporter: Aldrin Leal
            Priority: Trivial


  While doing commons-lang stuff, I found the repetitive nature of
Builder stuff. Therefore, i decided to:

 a) Create a SingleBuilder (for ToString / HashCode) and a
DualBuilder (CompareTo / Equals) interface, and make their classes
implementing;
 b) Create a SingleBuilderVisitor and DualBuilderVisitor;
 c) Do the proper wiring, while creating new constructors using the visitors;
 d) Create new tests and ensuring javadoc plays nice along;

 There's a patch attached in this e-mail, done against the latest
svn STABLE url for 2.2
(http://svn.apache.org/repos/asf/jakarta/commons/proper/lang/branches/LANG_2_2_X/)

 There might be errors, but methinks it's a great idea to declare a
constant like this in your source code.

 private static final EQUALS_VISITOR = new DualBuilderVisitor() {
          public void visit(DualBuilder builder, Object lhs, Object rhs) {
             Type lhsObj = (Type) lhs;
             Type rhsObj = (Type) rhs;
              builder.append(lhsObj.getId(),
rhsObj.getId()).append(lhsObj.getName(), rhsObj.getName());
          }
 };

 And then, declare and instantiate builders like as, say:

 public boolean equals(Object anotherObj) {
  return new EqualsVisitor(EQUALS_VISITOR, this, anotherObj);
 }

 Please note this implementation, overrall, also lets you easily use
a single visitor for either equals and compareto, thus creating a
single point of management for all your
field-maintenance-in-value-objects-needs.

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