Processing 1.0 - Processing Discourse

We closed this forum 18 June 2010. It has served us well since 2005 as the ALPHA forum did before it from 2002 to 2005. New discussions are ongoing at the new URL http://forum.processing.org. You'll need to sign up and get a new user account. We're sorry about that inconvenience, but we think it's better in the long run. The content on this forum will remain online.

‹ Previous Topic | Next Topic ›

Pages: 1

ClassLoader (Read 1408 times)

till

ClassLoader
Oct 10^th, 2005, 2:28pm

Hey board,

Since this is my first post, I have to say, that Processings seems to be a great tool for graphics and visualization...
But as always I have a little problem at the moment, and do not really know where I should post it, so I post it here:

I want to instantiate a class which's name is determined by

String s;

[...]

println(s);
--> "Grain"

Object o = new "Class of type s";

---------snap--------

I already know how to instantiate a ClassLoader (think, it should work with this tool), but I cannot do this in processing:

-----snip----
ClassLoader cLoader = new ClassLoader();
--> The constructor "ClassLoader();" in type "java.lang.ClassLoader" has protected access and is not accessible here.
-----snap----

So, how else should I manage this?

btw. I don't wan to write an applet...

thanx in advance
Till

fry YaBB Moderator Offline Posts: 2623 mass, usa	Re: ClassLoader Reply #1 - Oct 10^th, 2005, 4:53pm you need to read more about how ClassLoader works. you can't create one like that because the constructor has "protected" access. generally you probably need to make your own subclass, or use: ClassLoader sys = ClassLoader.getSystemClassLoader();

till

Re: ClassLoader
Reply #2 - Oct 11^th, 2005, 3:44pm

Hi fry, all,

thanx for moving my post to the right thread, and answering that fast.
After using yout hint, I still get a new (for me very strange) problem.

-- snip --
class Test {
Test() {
}
}
void setup(){
[...]
Test t = new Test();
// print the Class name:
println(t.getClass().toString());

ClassLoader sys = ClassLoader.getSystemClassLoader();
try {
sys.loadClass("Test").newInstance();
} catch (Exception e) {
println("Problem...: "+e);
}
}
-------snap--------
When I do this in Processing, I get a strange classname (something like
"Temporary_2127_8958$Grain"
) which is not the classname I was suspecting...
And of course it does not work properly...

I think, it is something which relates to the processing environment, right?
How to prevent this?
I definitely need to instantiate a class setermined by its used classname...
("Test" in this case)

Any hints anyone?

Thanks in advance
Till

till YaBB Newbies Offline Posts: 9	Re: ClassLoader Reply #3 - Oct 14^th, 2005, 10:37am no one knows about this? thats a pitty, really... i think it is because of the use of jikes here... is there a jikes-specific ClassLoader anywhere accessible? __ till

fry

Re: ClassLoader
Reply #4 - Oct 14^th, 2005, 3:38pm

the temporary name comes from how things are compiled inside processing, because you're not specifying a class name, it needs to give you a temporary one. and in fact, behind the scenes it's using its own classloader to handle this, so if you want to see how that works, you can dig in the processing source (dev.processing.org/source).

what is it you're trying to do with the class loader? is it not something that could be handled for Class.forName() or something like that? using a ClassLoader is very low level and almost always unnecessary.

till

Re: ClassLoader
Reply #5 - Oct 21^st, 2005, 1:56pm

I want to dynamically instatiate classes from out of a String containing the class name... (send via OSC and received with oscP5)...

Supposed I have the following classes defined in Processing's edit window:

class Grain {
Grain () {
}
}

class GBox extends Grain {
GBox () {
}
}

----snap----

I want to do something like

String classname = "GBox"
Grain act = null;

// this works (as expected)

if (classname.equals("GBox")) {
act = new GBox();
}

// this not

try {
Class grainClass = Class.forName(classname);
act = (Grain) grainClass.newInstance();
} catch (Exception e) {
println(e);
return;
}

// prints "java.lang.ClassNotfoundException: GBox"

So: how to find the correct name?

Thanx for any help
Till

JohnG

Re: ClassLoader
Reply #6 - Oct 21^st, 2005, 4:09pm

I've no idea if this'll work, but you could try
Code:


String theClass=this.getClass().getName() + NameOfClassYouWant

to get the correct class.

Edit: Actually, you may need to add a "$" between the two.

Here's some code that prints the "real" classnames:

Code:

class foo
{
  foo()
  {
    println(this.getClass().getName());
  }
}

foo f;

void setup()
{
  size(200,200,P3D);
  println(this.getClass().getName());
  f=new foo();
}

Prints:
Code:

Temporary_4895_9691
Temporary_4895_9691$foo

till

Re: ClassLoader
Reply #7 - Oct 24^th, 2005, 5:47pm

thanx john, fry for your help...

--------snip------------
class foo {
foo() {
}

}

void setup() {

size(200,200);

String fooName = "foo";

try {
foo theFoo = (foo) Class.forName(this.getClass().getName() + "$" + fooName).newInstance();
} catch (Exception e) {
println(e);
}
}
---------snap------------

unfortunaltely this does not create the desired Objects, but prints a
--- snip ---
java.lang.InstantiationException: Temporary_9757_7229$foo
--- snap ---

(btw: how to insert code properly into this forum?)

regards
Till

till YaBB Newbies Offline Posts: 9	Re: ClassLoader Reply #8 - Nov 4^th, 2005, 2:57pm Hey all, I'm still interested in a solution of the above-described problem... So if someone could point me into the right direction, or just tells me, how to manage this, give me a hint, please... have a nice day Till

fry

Re: ClassLoader
Reply #9 - Nov 4^th, 2005, 10:14pm

my guess is that the InstantiationException comes from trying to create an inner class, which probably has weird dynamics to it. especially because you haven't set the constructor or the class itself to be "public".

to get around the "temporary" thing, explicitly name the sketch. ie. if your sketch is named "poo" do this:

public class poo extends PApplet {

however, once you've done that, you're on your own as far as making sure that the code is proper java, and that the name is in sync with the sketch name.

for the other classes, you're best off creating them as .java files. so create a new tab, name it "something.java" and it'll be just straight java code (no preprocessor anymore), and not an inner class. in doing so, you'll need to pass the PApplet object to the other class (in its constructor, for instance), in order to make things like drawing work properly. keep in mind this is all fairly messy/advanced stuff...

till YaBB Newbies Offline Posts: 9	Re: ClassLoader Reply #10 - Nov 11^th, 2005, 5:13pm Hey fry, all, thanx, I'll look at it, soon have a nice day Till

Pages: 1

‹ Previous Topic | Next Topic ›