Re: multiple inheritance in Java

From:

Eric Sosman <esosman@comcast-dot-net.invalid>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 02 Jul 2013 00:30:18 -0400

Message-ID:

<kqtkmm$4ac$1@dont-email.me>

On 7/1/2013 10:32 PM, Stefan Ram wrote:

markspace <markspace@nospam.nospam> writes:

With private fields, you can enforce some constraint on color and
position. Without it, you'll constantly have to check in every method
if those constrains are still valid or not.

I only deal with cases where no additional constraints are required.

So, just a struct?

There's other reasons. Public final fields aren't thread safe, for
example, so you're encouraging bad style, imo.

   I don't actually know what it means for a field to be thread
   safe. But I was talking about final fields (see also below).
   Those fields are only written to in the constructor.

Yeah, but they are references to objects with non-final fields.
If thread T1 does cp.color.setR(42) and T2 does r=pc.color.getR()
while cp and pc refer to the same ColorPoint instance (or to distinct
ColorPoint instances that refer to the same Color instance), you've
got a race.

You also allow any arbitrary changes to your class this way, and forgo
encapsulation. This also seems bad style.

   A class in Java can only be changed by the programmer.
   Possibly you are speaking of an instance of that class.
   Since the fields I gave where final (see also below),
   they cannot be changed outside of the constructor.

     A non-final class in Java can only be changed by *any*
programmer, via the mechanism of extension. For example,
I might write

    /**
     * A specialized ColorPoint that automatically adjusts
     * its "saturation" depending on the distance from a
     * designated origin position.
     */
    public class RadialColorPoint extends ColorPoint {
        ...
    }

.... and suddenly I've got constraints not anticipated by the
original author -- without changing a single line of his code.
With (overridable) accessors I could manage those constraints;
with exposed fields I could not.

What's your goal here?

It seems best to me to implement something this way, and I wonder
whether I have missed potential issues with it.

"It seems best" isn't a goal, it's at most a whimsy.

--
Eric Sosman
esosman@comcast-dot-net.invalid