Re: Using abstract class that implements interface

From:

Lew <noone@lewscanon.com>

Newsgroups:

comp.lang.java.programmer

Date:

Sat, 18 Apr 2009 22:41:24 -0400

Message-ID:

<gse30k$unf$1@news.albasani.net>

Tom Anderson wrote:

'Programming to an interface' does *not* refer to the syntactic
construct of an interface, but the semantic idea of a set of defined,

It does refer to the syntactic construct of an interface when it comes to best
practices in Java.

public methods. What in Smalltalk would be called a 'protocol'. An
abstract base class can define an interface for this purpose just as
well as an interface (IYSWIM).

Arne Vajh??j wrote:

It can.

And it does for all the languages that does not have a special
syntax for interfaces.

But an explicit interface syntax makes it a bit more stringent,
because it is enforced that it does not carry any implementation.

The best practice in Java is to program to the interface according to Java's
definition of "interface". See Bloch, /Effective Java/, Item 18, "Prefer
interfaces to abstract classes".
Some of his points:

Existing classes can be easily retrofitted to implement a new interface.
Interfaces are ideal for defining mixins.
Interfaces allow the construction of nonhierarchical type frameworks.
Interfaces enable safe, powerful functionality enhancements

He goes on in that chapter to recommend implementating an interface with an
abstract class to provide default method implementations, and to publish the
interface to client code, just as the OP did.

--
Lew