[java] LooseCoupling rule: Extend to cover user defined implementations and interfaces

[linusjf]

Is your feature request related to a problem? Please describe.
The rule LooseCoupling flags implemented classes when interfaces suffice. It prescribes coding against an interface as against implementor classes.
It currently checks for Collections API classes. Please extend the rule so that developers can specify user-defined classes as well.

Describe the solution you'd like
The rule must be made configurable so that users can define interfaces and implementor classes from their application's source base.

Describe alternatives you've considered
None that I know of.

Additional context

None.

Other issues for the same rule:

• [java] LooseCoupling must ignore class literals: ArrayList.class #2464
• [java] LooseCoupling false-positive with methods only available on concrete collection class #1218

[linusjf]

A property is needed to optionally flag the use of var when instantiating a concrete type.

[linusjf]

#2847 (comment)

Add a property to extend the rule to local variables.

[adangel]

With PMD7 there is a new property now "allowedTypes" for the rule LooseCoupling.
This property by default allows java.util.Properties.

While working on #3657 I found, that we should also allow java.util.Stack - while stack is a collection, you can't use the List interface, if you use the stack-methods (push, pop). That's very similar like Properties, which is a Map, but a Map doesn't have "getProperty".

@oowekyala Wdyt?

[oowekyala]

Stack is a tricky case. Its own documentation recommends using the Dequeue interface and ArrayDequeue as an implementation. Maybe we could disallow it to force migration. Stack extends Vector so there are good reasons to get rid of it.

A solution I like more, however, would be to make LooseCoupling allow Stack, but to create another rule that recommends migrating to Dequeue. That new rule could subsume UseArrayListInsteadOfVector, ReplaceVectorWithList and other rules like ReplaceHashtableWithMap and ReplaceEnumerationWithIterator.

[adangel]

This has been fixed with PMD 7.0.0-rc1.