[COLLECTIONS-251] improving static factory methods for static importability, conistency

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.2
• Fix Version/s: 4.0-alpha1, 4.0
• Component/s: Bag, BidiMap, Buffer, Collection, Comparator, Core, Functor, Iterator, KeyValue, List, Map, Set
• Assignee: Unassigned
• Reporter: Stephen Kestle
• Created: 03/May/07 01:38
• Updated: 09/Nov/14 14:31
• Resolved: 20/Jul/11 14:46

Description

Commons Collections uses the singleton "getInstance()" pattern and extends it to allow parameters etc to be passed in. decorate() serves a similar purpose.

I propose replacing both of these with getClassName() for the following reasons:
1. Static imports would mean that TruePredicate.getInstance() would be replaced with getTruePredicate(). getInstance() cannot be statically imported, because it is reduced to one class' getInstance(), where we are likely using many.
2. It gives subclasses a way to avoid compiler issues - COLLECTIONS-243 compile problems are generally because the compiler can't choose between Collection<T> and Set<T>. Doing this change completely avoids this issue - even if there is a workaround, this makes life a lot easier (different compilers - eclipse - will allow things that the Sun one won't).
2.1 Overridden and overloaded static methods are a really bad idea
2.2 No confusion about what class is being instantiated
2.3 As our methods become more useful in the generic sense, the compiler issues increase until you hit something that just won't work
3. Simple migration path - those using TruePredicate.getInstance() can switch to PredicateUtils.truePredicate() before updating to this version.
4. Allows a more consistent user environment. Following the current pattern means that most people will have MyTransformer.getInstance(), while using TransformerUtils.nopTransformer().

Our work will be made a lot easier if we make this change.

Issue Links

• breaks: COLLECTIONS-378 Incorrect links in JavaDoc