ClassNotFoundException when extending PApplet

clankill3r · July 2014

As an experiment i try to extend PApplet and run that.

This is the library class:

public class Problessing extends PApplet {

    static public void main(final String[] args) {
        PApplet.main(args);
    }
}

This is my processing sketch:

import nl.doekewartena.problessing.*;

static final void main(String[] args) {

  final String sketch = Thread.currentThread()
    .getStackTrace()[1].getClassName();

  println(sketch);

  Problessing.main(sketch+".Test");
}



class Test extends Problessing {

  void setup() {
    println("ok");
  }
}

Instead of Problessing.main(sketch+".Test"); I also tried Problessing.main("Test"); but still i get ClassNotFoundException.

Can someone help?

clankill3r · July 2014

I'm a bit further, i had to use a $ instead of a dot. In processing the class is found now but i get a "java.lang.instantiationException".

static final void main(String[] args) {

  final String sketch = Thread.currentThread()
    .getStackTrace()[1].getClassName();  

  Problessing.main(sketch+"$Test");
}

In intelliJ it works now.

import nl.doekewartena.problessing.Problessing;

public class Test extends Problessing {

    public static void main(String args[]) {

        Problessing.main("Test");
    }


    public void setup() {
        println("ok");
    }

}

Someone an idea why processing can't make the instance?

GoToLoop · July 2014

Gonna repost what I replied in private here to help context:

1st, I don't see any logic why any1 would wanna extend PApplet. Not even the other Processing libraries do that! A simple import would suffice IMO! :P

But if you insist on that... you're gonna need your own static main(String[] args) {}. So you can force a call to Problessing.main("") in place of the original PApplet.main("")!

Since your Problessing library is actually a hacked fork of the original PApplet,
both you and any1 trying to use it gotta struggle against Processing's pre-processor!

The pre-processor wraps up all ".pde" tabs w/ public class Name_of_1st_PDE_Tab extends PApplet {}.
Therefore, you can't change it to extends Problessing {}! And even Problessing.main("") gonna fail!

As long Processing's pre-processor is in the way, your project is doomed! :o3

quark · July 2014

The difference between the 2 examples in your last comment is that

in Processing you are trying to instantiate an inner class

in IntelliJ you are instantiating a top-level class

I suggest you make the Test class a top level class by declaring it static and see what happens

import nl.doekewartena.problessing.*;

public static final void main(String[] args) {
  Problessing.main("Test");
}

public static class Test extends Problessing {

  void setup() {
    println("ok");
  }
}

EDIT posted before I saw GoToLoop's comment and became aware PMs

GoToLoop · July 2014

Seems like @quark got ahead of what I was already fomenting as a possible solution.
Although a heavy boilerplate to ask any regular Processing programmer to paste before using a "library"!

Below's the general recipe idea:

// forum.processing.org/two/discussion/6256/
// classnotfoundexception-when-extending-papplet

static final void main(final String[] args) {
  PApplet.runSketch(append(args, ""), new MyApp());
}

static final class MyApp extends PApplet {
  void setup() {
    println("OK!");
    exit();
  }
}

And now the same above adapted to the new fork library:

// forum.processing.org/two/discussion/6256/
// classnotfoundexception-when-extending-papplet

import nl.doekewartena.problessing.*;

static final void main(final String[] args) {
  Problessing.runSketch(append(args, ""), new MyApp());
}

static final class MyApp extends Problessing {
  void setup() {
    println("Hacked!");
    exit();
  }
}

P.S.: Doing so, we won't be able to use multiple tabs, since they would be PApplet's nested classes!

quark · July 2014

Although a heavy boilerplate to ask any regular Processing programmer to paste before using a "library"!

I agree but if it just an experiment - it has some interest.

I suggest that the public access specifier is used - then it is not dependent on the pre-processor doing the job. After all we have no guarantee that the pre-processor functionality won't change.

GoToLoop · July 2014

Alternative version. Although even more boiler-plate: >-)

// forum.processing.org/two/discussion/6256/
// classnotfoundexception-when-extending-papplet

static final void main(final String[] args) {
  final String sketch = Thread.currentThread()
    .getStackTrace()[1].getClassName();

  PApplet.main(append(args, sketch + "$MyApp"));
  //PApplet.runSketch(append(args, ""), new MyApp());
}

public static final class MyApp extends PApplet {
  void setup() {
    println("OK!");
    exit();
  }
}

GoToLoop · July 2014

I suggest that the public access specifier is used.

I'm posting a Processing's IDE oriented recipe for regular programmers. :\">
I don't wanna make the recipe even more complicated than it already is! (~~)
After all, Processing's pre-processor already place public in almost anything. :\">
Any user for other pro IDE's already knows which ".pde" modifications gotta be done anyways! ;))

P.S.: My latest boiler-plate experiment indeed demands the public inclusion, so reflection works!
On the other hand, directly instantiating the hacked class and passing that to runSketch() doesn't demand public! :P

GoToLoop · July 2014

Newer boilerplate version. This time, besides not needing the name for the top-class,
we don't need for its nested class either when invoking PApplet.main("")! Check it out: \m/

// forum.processing.org/two/discussion/6256/
// classnotfoundexception-when-extending-papplet

public static final void main(final String[] args) {
  final String nested, sketch = Thread.currentThread()
    .getStackTrace()[1].getClassName();

  try {
    nested = Class.forName(sketch)
      .getClasses()[0].getName();
  }

  catch (final ClassNotFoundException e) {
    throw new RuntimeException(e);
  }

  PApplet.main(append(args, nested));
  //PApplet.runSketch(append(args, ""), new MyApp());
}

public static final class MyApp extends PApplet {
  void setup() {
    println("OK!");
    exit();
  }

  void draw() {
    background(-1);
  }
}

clankill3r · July 2014

Damn, it really sucks that other classes can't be used since they will be nested. Good thing is it still works in eclipse and IntelliJ.

What i can do now for example is this:

import nl.doekewartena.problessing.*;

public class Test3 extends Problessing {

    public static void main(String args[]) {
        Problessing.main("Test3");
    }

    public void setup() {
        size(200, 200, MM); // PDF will be this size in MM
        noiseMode(PERLIN); // choose between VALUE and PERLIN noise
    }

    public void draw() {
        background(noise(frameCount*0.02f)*255);

        stroke(Red); // all CSS color names are working
        fill(DarkCyan);

        strokeWeight(3, MM);

        // fmouseX is frameMouseX, this can give negative values
        // and values > width. This way the ellipse won't get stuck at a edge but can leave the frame now
        ellipse(fmouseX, fmouseY, 20, 20);

    }

}

Btw, where on github can i find the code of the precompiler? I would like to have a look at it.

Howdy, Stranger!

Categories

In this Discussion

ClassNotFoundException when extending PApplet

Best Answer

Answers