Re: What's the use of private?

From:

Lew <lew@lewscanon.com>

Newsgroups:

comp.lang.java.programmer

Date:

Sun, 17 Feb 2008 10:36:47 -0500

Message-ID:

<fY2dnf07FaISySXanZ2dnUVZ_q3inZ2d@comcast.com>

Jeff.M wrote:

On Feb 17, 10:05 am, Lew <l...@lewscanon.com> wrote:

Jeff.M wrote:

On Feb 17, 9:55 am, r...@zedat.fu-berlin.de (Stefan Ram) wrote:

"Jeff.M" <Mott.J...@gmail.com> writes:

what's the use of private?

http://en.wikipedia.org/wiki/Information_hiding

That page doesn't answer my question. But thanks for responding.

Actually, that page explains precisely the reason for private methods and
variables, which is precisely what you asked for.

--
Lew

That page explains information hiding in general. My question is about
private versus protected. Both already support the principle of
information hiding. The only difference is that protected members are
accessible also to sublcasses (any code that is responsible for the
implementation of the object).

And, as that article mentions, inheritance (i.e., protected access) breaks
encapsulation. The advantage of private accessibility is that they are not
accessible to subclasses.

The authors of Design Patterns discuss the tension between inheritance and encapsulation at length and state that in their experience, designers overuse inheritance (Gang of Four 1995:20). The danger is stated as follows:

"Because inheritance exposes a subclass to details of its parent's implementation, it's often said that 'inheritance breaks encapsulation'". (Gang of Four 1995:19)

[edit]

The principles discussed in that article are exactly the answer to your
question. Apply what it says to the notion of private vs. protected (or even
package-private) and you have your answer.

--
Lew