declaration of array of objects, which method?

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000gbt

declaration of array of objects, which method?

in Programming Questions • 2 years ago

Hello,

I discover the world of Processing, and I'm thrilled by it.

I have some questions regarding arrays of objects, the way to create them, and eventually discuss how to make arrays of variable lenght.

my way of declaring an array of object until now was:

suppose of course that the class Branch is defined

int number_of_instances = 100; // size of the array to be created
Branch[] _branchArr = new Branch[number_of_instances]; // declaration of the array
for (int i=0; i<number_of_instances; i++) {
_branchArr[i] = new Branch(); // constructor EDIT: I corrected the typo // found by phi.lho as described below
}

Looking thru some source code at abandonnedart.com, I saw this form of declaration for arrays of objects:

Branch[] _branchArr = {};
// below the code is meant to create one new object in the array
// it could be put in a for loop as above
Branch br = new Branch();
_branchArr = (Branch[])append(_branchArr, br);

in the first line I suppose {} stands for the NULL ensemble, that is an array is created that contains no element at all, am I right?

then this method seems to provide an easy way to make arrays of variable lenght, if needed (unlike my method which fix a number_of_instances ). (using also shorten() or expand() ).

Then I saw ArrayList existed, and it's purposes was to create array of changing size.

so my questions are:

- are there other methods to create arrays of objects, that would be interresting?

- is one method "better" than another to create arrays of objects? especially if one wants a variable lenght of array?

this last is probably too advanced:

- is there a risk to run out of memory, or else, creating to many objects (I guess so), and is there a way of detecting such a danger, and then provide to the user a dedicated limit, corresponding to it's own personnal situation?

Best regards,

Laurent.

Replies(2)

PhiLho

Re: declaration of array of objects, which method?

2 years ago

OK, for the record, you made a typo (I suppose) in the first code snippet, it should be _branchArr[i] = new Branch();
Next, the method append() is specific to Processing, and, I fear I have to write, very inefficient and often confusing to newbies, which is finally opposite of its initial goal (ie. providing a non-object, non-boxing alternative to ArrayList).
Basically, I would advise just to forget it...

Several other methods to create arrays can be made, but they would be convoluted, inefficient, etc. ArrayList is the most used in the Java world, to make a variable length array. Note that if you really need an array, there is a method to convert an array list to a simple array.

One drawback of array lists is that they need to wrap primitive objects (char, int, float, boolean, etc.) in objects, thus making the storage bigger than with a simple array. Otherwise, they are perfect for storing objects (from String to PVector, etc.).
Before Java 1.5, the syntax was more cumbersome, having to cast a.get(i) to the type of object (or primitive), but now you can create array lists with type (eg. ArrayList<PVector> or ArrayList<Integer>) and Java even take care of auto-unboxing (extracting an int out of an Integer, for example).

Out of Memory error (OOM, as often said): it is in general not a real concern in Processing, at least because of number of objects. The size of objects might matter (eg. loading a bunch of image files). IIRC, each base object reference (only references are stored in array [lists]) takes 24 bytes. Base Processing can handle megabytes, and you can set up memory in Preferences, to 1 or 2 GB (might have some issues beyond that).
Having a million of particles, for example, shouldn't stress much memory (much more CPU!).

000gbt

Re: declaration of array of objects, which method?

2 years ago

Thanks a lot phil.lho for your very complete answer, you gave me all the informations I needed!

I'll use the ArrayList, and forget about the append() method.

And you are right about the typo too, sorry...

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