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From Stephen Williams <scient...@gmail.com>
Subject Re: Pointers
Date Fri, 28 Jan 2011 23:00:01 GMT
True, you shouldn't synchronize on any object that A) you want to change and
B) can only be changed by being replaced by a newly constructed object.  If
Integer, for instance, had a setter method, then it could still have been
used in this way.  However, it seems to be immutable.  I generally just
create something like the following to synchronize:
Object lockArg;

A method I use for returning more than one value would be useful here also:
Integer[] arg = new Integer[](1);
arg[0] = new Integer(5);
// or with autoboxing:
arg[0] = 5;

void funkyChanger(Integer[] arg) {
    synchronized (arg) { ...  arg[0]++; ... }
}

Is there a problem with this as a general idiom?  You could use naming to
signal the nature as indirect vs. logically an array.  And, a future version
of Java could use syntactic sugar for 'ref' to do this by autoboxing the 1
deep array also.

About returning tuples:
Returning more than one value from a method has two reasonable solutions
that seem minimal for their use cases: returning a tuple as a single value
or making one or more calls to a callback method.  The simplest case is when
multiple values need to be returned.  While callbacks have their place when
you need to trigger more operations incrementally, they are cumbersome as
you need to define a class and provide an implementation, although the
latter can be an anonymous implementation.  Many have complained about the
lack in Java of pair<>, however with the object reference system, it is easy
to do this with arrays.  If the types are all the same, like String[], this
is completely typesafe.  Otherwise, you can use Object[].  You can also
define a return type class to fill, however that is cumbersome.  In addition
to Object[], a TreeMap can be a good solution, especially when more than a
few parameters are needed and they might change over time.

Stephen

On Fri, Jan 28, 2011 at 2:21 PM, James Ring <sjr@jdns.org> wrote:

> Hey,
>
> On Fri, Jan 28, 2011 at 2:01 PM, Stephen Williams <scienteer@gmail.com>
> wrote:
> > All objects are passed as references in Java.
> > All fundamental scalar types have Object wrapped versions.
> > An argument that is meant to be modified just needs to be an object
> > reference.
> >
> > So, you can simply go from:
> > void funkyReader(int arg) { arg++; }
> > to:
> > void funkyChanger(Integer arg) { arg++; }
> >
> > If it needs to be threadsafe, simply synchronize on the object everywhere
> it
> > is used.
>
> It's a bad idea to synchronize on the wrapper objects of primitive
> types: http://www.theothertomelliott.com/node/40
>
> This includes Integers.
>
> Regards,
> James
>
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