Reassigning an array of a class.

[MS]

Hi,

In my Genetic Algorithm program, I have a class called Genome. Another
class called GA has a class variable called 'population' which is an array
of type Genome.

One of the methods in GA, called CreateNextGener ation(), creates a local
array of class Genome called 'nextGeneration ', and at the end of that
method I want the class variable 'population' to hold the array
'nextGeneration '.

Is it as simple as?

population = nextGeneration;

At the moment class Genome contains a copy method, and I have a loop which
copies all the Genomes in 'nextGeneration ' to 'population' (the 2 arrays
are always the same size). This is obviously ineffecient, but I was
worried about what memory and garbage collection overheads there would be
it I used the line:

population = nextGeneration;

Should using this line be ok?

Many thanks,

MS

[Eric Sosman]

Re: Reassigning an array of a class.



MS wrote:[color=blue]
> Hi,
>
> In my Genetic Algorithm program, I have a class called Genome. Another
> class called GA has a class variable called 'population' which is an array
> of type Genome.
>
> One of the methods in GA, called CreateNextGener ation(), creates a local
> array of class Genome called 'nextGeneration ', and at the end of that
> method I want the class variable 'population' to hold the array
> 'nextGeneration '.
>
> Is it as simple as?
>
> population = nextGeneration;
>
> At the moment class Genome contains a copy method, and I have a loop which
> copies all the Genomes in 'nextGeneration ' to 'population' (the 2 arrays
> are always the same size). This is obviously ineffecient, but I was
> worried about what memory and garbage collection overheads there would be
> it I used the line:
>
> population = nextGeneration;
>
> Should using this line be ok?[/color]

Yes. Neither `population' nor `nextGeneration ' is
actually an array; both are references to array objects.
Here's a crude schematic:

population -> [a,b,c]

nextGeneration -> [x,y,z]

When you execute `population = nextGeneration' you redirect
the upper arrow to point to the lower array object. If there
are no other references to the upper array, it becomes
eligible for garbage collection.

--
Eric.Sosman@sun .com

[MS]

Re: Reassigning an array of a class.

> Yes. Neither `population' nor `nextGeneration ' is[color=blue]
> actually an array; both are references to array objects.
> Here's a crude schematic:
>
> population -> [a,b,c]
>
> nextGeneration -> [x,y,z]
>
> When you execute `population = nextGeneration' you redirect
> the upper arrow to point to the lower array object. If there
> are no other references to the upper array, it becomes
> eligible for garbage collection.[/color]

Many thanks Eric.

[Nigel Wade]

Re: Reassigning an array of a class.

Eric Sosman wrote:
[color=blue]
>
>
> MS wrote:[color=green]
>> Hi,
>>
>> In my Genetic Algorithm program, I have a class called Genome. Another
>> class called GA has a class variable called 'population' which is an[/color][/color]
array[color=blue][color=green]
>> of type Genome.
>>
>> One of the methods in GA, called CreateNextGener ation(), creates a local
>> array of class Genome called 'nextGeneration ', and at the end of that
>> method I want the class variable 'population' to hold the array
>> 'nextGeneration '.
>>
>> Is it as simple as?
>>
>> population = nextGeneration;
>>
>> At the moment class Genome contains a copy method, and I have a loop[/color][/color]
which[color=blue][color=green]
>> copies all the Genomes in 'nextGeneration ' to 'population' (the 2 arrays
>> are always the same size). This is obviously ineffecient, but I was
>> worried about what memory and garbage collection overheads there would be
>> it I used the line:
>>
>> population = nextGeneration;
>>
>> Should using this line be ok?[/color]
>
> Yes. Neither `population' nor `nextGeneration ' is
> actually an array; both are references to array objects.
> Here's a crude schematic:
>
> population -> [a,b,c]
>
> nextGeneration -> [x,y,z]
>
> When you execute `population = nextGeneration' you redirect
> the upper arrow to point to the lower array object. If there
> are no other references to the upper array, it becomes
> eligible for garbage collection.
>[/color]

One important point though, is that after 'population = nextGeneration' both
population and nextGeneration refer to the *same* array.

If your CreateNextGener ation() method simply "populates" the array
nextGeneration, then you will also change the data which population refers
to. You need to make sure that CreateNextGener ation() creates a new array.

--
Nigel Wade, System Administrator, Space Plasma Physics Group,
University of Leicester, Leicester, LE1 7RH, UK
E-mail : nmw@ion.le.ac.u k
Phone : +44 (0)116 2523548, Fax : +44 (0)116 2523555

[MS]

Re: Reassigning an array of a class.

>> Yes. Neither `population' nor `nextGeneration ' is[color=blue][color=green]
>>actually an array; both are references to array objects.
>>Here's a crude schematic:
>>
>> population -> [a,b,c]
>>
>> nextGeneration -> [x,y,z]
>>
>>When you execute `population = nextGeneration' you redirect
>>the upper arrow to point to the lower array object. If there
>>are no other references to the upper array, it becomes
>>eligible for garbage collection.
>>[/color]
>
>
> One important point though, is that after 'population = nextGeneration' both
> population and nextGeneration refer to the *same* array.
>
> If your CreateNextGener ation() method simply "populates" the array
> nextGeneration, then you will also change the data which population refers
> to. You need to make sure that CreateNextGener ation() creates a new array.[/color]

Thanks.

CreateNextGener ation() does create a new local array, nextGeneration, and
fills it with new Genomes. It does some stuff and then finally reassigns
population: 'population = nextGegeration; '.

Cheers,

MS