Loading class files, weird behavior.

KellyKetchup

Hi, I would like to load 'extensions' into my sketch dynamically. First by just loading .class files from my file system, later by loading them from a database. The problem is that I am not a java-wizard: I have looked up some snippets on how to use URLClassLoader to load a local .class file into my sketch, I just used a test .java file that I compiled and placed in my home folder. Loading goes without incidents as it seems, but when I try to access any of the methods (both static and non-static) or instantiate the class I get bathed in weird exceptions. Here is an abbreviated version of the code I am testing around with:

 //sketch_123.pde

import java.net.*;
import java.lang.reflect.*;

void setup(){
  File file = new File("/home/user/");

  try {
    URL url = file.toURL();
    URL[] urls = new URL[]{url};

    ClassLoader cl = new URLClassLoader(urls);
    Class cls = cl.loadClass("test");

    Object o = cls.newInstance();
    //InstantationException !!!

    Method m = cls.getDeclaredMethod("run");
    //NoSuchMethodException !!!

  } catch (MalformedURLException e) { print("Your URL was faulty.\n");
  } catch (ClassNotFoundException e) { print("The URL was not found.\n");
  }
}

And here is the test.java file that I simply compile with javac -g test.java -d /home/user

//test.java
//no package

public class test{
  public test(){}

  public static void run(){
  }

  public String get(){
  return "Hello World!"; 
  }
}

You can see the two exceptions I get while testing around with this commented in the sketch. I can get the methods of 'cls' by calling getDeclaredMethods(), I even made a loop that prints their names, but as soon as I try to invoke the method object I get an illegalaccessexception. Having found no possibly related answer to this on google I am starting to think it has something todo with processing and how it sets up the sketch and all that. Please help.

GoToLoop

Never used getDeclaredMethod() before but getDeclaredField(). 1 tiny example below:

/**
 * Enclosing Class Instance Reference (v1.02)
 * by GoToLoop (2014/May)
 *
 * stackoverflow.com/questions/763543/in-java-how-do-i-access-
 * the-outer-class-when-im-not-in-the-inner-class
 */

void setup() {
  println(this);
  println(new Inner().q == this);
  exit();
}

class Inner {
  PApplet q;

  Inner() {
    try {
      q = (PApplet) getClass().getDeclaredField("this$0").get(this);
      println(q);
    }

    catch (ReflectiveOperationException cause) {
      throw new RuntimeException(cause);
    }
  }
}

Also there's this thread where I've messed a little more w/ that:
http://forum.processing.org/two/discussion/5065/variable-names-using-another-variable

KellyKetchup

Instead of using the loaded class I have now simply added the .java file as a tab. I use .getClass() on an instance of test to recreate the situation I had before.

...
test inst = new test();

Class tclass = inst.getClass(); //tclass == cls (*in the first post)

Constructor tconst = tclass.getConstructor(); //NoSuchMethodException !!!
...

This seems especially weird. Even tho I know that I have declared a public no-args constructor for class test I can not get it.

GoToLoop

Have you already attempted getDeclaredConstructor() instead of simply getConstructor()? #-o
http://docs.oracle.com/javase/8/docs/api/java/lang/Class.html#getDeclaredConstructor-java.lang.Class...-

KellyKetchup

Have you already attempted getDeclaredConstructor() instead of simply getConstructor()?

Yes. And because both versions don't work I am doing this:

    test f=new test();

    //f.getClass().getDeclaredConstructor();

    Constructor<test> a=null;

    for(Constructor<?> c:f.getClass().getDeclaredConstructors()){ 
      print(c.toString()+"\n"); 
      a=(Constructor<test>)c; 
      break; }

    test g=(test) a.newInstance(); //InstantiationException !!!

KellyKetchup

Okay, so I started up eclipse just now and tried the very same thing from above and guess what? In a separate java application everything works fine. Wow, lots of time wasted now. I guess I am just going to continue working on this in eclipse? :o

GoToLoop

I've adapted the code I had about Field into Constructor and it worked:
http://forum.processing.org/two/discussion/5065/variable-names-using-another-variable

/**
 * Get Constructor Instantiation (v1.1)
 * by GoToLoop (2014/Jun)
 *
 * forum.processing.org/two/discussion/5678/
 * loading-class-files-weird-behavior-
 *
 * forum.processing.org/two/discussion/5065/
 * variable-names-using-another-variable
 */

import java.lang.reflect.Constructor;

void setup() {
  Constructor c = getClassConstructor(HashMap.class);
  HashMap h = (HashMap) getInstance(c);
  println(h);

  Constructor<PVector> pc = getClassConstructor(PVector.class);
  PVector p = getInstance(pc);
  println(p);

  Table t = getInstance(getClassConstructor(Table.class));
  println(t);

  exit();
}

static final <T> Constructor<T> getClassConstructor(Class<T> c) {
  try {
    return c.getDeclaredConstructor();
  }

  catch (NoSuchMethodException e) {
    println(e);
    return null;
  }
}

static final <T> T getInstance(Constructor<T> c) {
  try {
    return c.newInstance();
  }

  catch (InstantiationException e) {
    throw new RuntimeException(e);
  }

  catch (IllegalAccessException e) {
    throw new RuntimeException(e);
  }

  catch (java.lang.reflect.InvocationTargetException e) {
    throw new RuntimeException(e);
  }
}