AssertionError occurred on box2d's step method

[helloscoopa]

When i add some JointPairs to the world there is a Assertion Error comming from the box2d's step method that called inside draw loop. here is the full code i've tried to understand by nature of code examples.

MainProgram.pde

import shiffman.box2d.*;
import org.jbox2d.common.*;
import org.jbox2d.dynamics.joints.*;
import org.jbox2d.collision.shapes.*;
import org.jbox2d.collision.shapes.Shape;
import org.jbox2d.common.*;
import org.jbox2d.dynamics.*;
import org.jbox2d.dynamics.contacts.*;

Box2DProcessing box2d;

ArrayList<Boundary> boundaries;
ArrayList<JointPair> pairs;


void setup() {
  size(640, 360);

  box2d = new Box2DProcessing(this);
  box2d.createWorld();

  pairs = new ArrayList<JointPair>();
  boundaries = new ArrayList<Boundary>();

  boundaries.add(new Boundary(width/4, height-5, width/2-50, 10));
  boundaries.add(new Boundary(3*width/4, height-50, width/2-50, 10));
}

void draw() {
  background(255);

  box2d.step();

  for (Boundary bounds : boundaries) {
    bounds.display();
  }

  for (int i=pairs.size()-1; i>0; i--) {
    pairs.get(i).display();
    if (pairs.get(i).isPairOffScreen()) {
      pairs.remove(i);
    }
  }
}

void mousePressed() {
  JointPair p = new JointPair(mouseX, mouseY);
  pairs.add(p);
}

Boundary.pde

class Boundary{
  float x,y,w,h;
  
  Body body;
  
  Boundary(float _x, float _y, float _w, float _h){
    x = _x;
    y = _y;
    w = _w;
    h = _h;
    
    //Define the shape
    PolygonShape ps = new PolygonShape();
    float box2dW = box2d.scalarPixelsToWorld(w/2);
    float box2dH = box2d.scalarPixelsToWorld(h/2);
    ps.setAsBox(box2dW,box2dH);
    
    //create body definition
    BodyDef bd = new BodyDef();
    bd.type = BodyType.STATIC;
    bd.position.set(box2d.coordPixelsToWorld(x,y));
    body = box2d.createBody(bd);
    
    //put all together
    body.createFixture(ps,1);
  }
  
  void display() {
    fill(0);
    stroke(0);
    rectMode(CENTER);
    rect(x,y,w,h);
  }

}

Box.pde

class Box {
  Body body;
  float w, h;

  Box(float x, float y) {
    w = 10;
    h = 10;

    makeBody(new Vec2(x, y), w, h);
  }

  void display() {
    Vec2 pos = box2d.getBodyPixelCoord(body);
    float a = body.getAngle();

    rectMode(CENTER);
    pushMatrix();
    translate(pos.x, pos.y);
    rotate(-a);
    fill(127);
    stroke(0);
    strokeWeight(2);
    rect(0, 0, w, h);
    popMatrix();
  }

  boolean isOffScreen() {
    Vec2 pos = box2d.getBodyPixelCoord(body);

    if (pos.x > width || pos.x < 0 || pos.y > height || pos.y <0) {
      killBody();
      return true;
    } else {
      return false;
    }
  }
  
  void killBody(){
    box2d.destroyBody(body);
  }

  void makeBody(Vec2 center, float _w, float _h) {

    //create shape here
    PolygonShape ps = new PolygonShape();
    float box2dW = box2d.scalarPixelsToWorld(_w/2);
    float box2dH = box2d.scalarPixelsToWorld(_h/2);
    ps.setAsBox(box2dW, box2dH);

    //create fixture definition
    FixtureDef fd = new FixtureDef();
    fd.shape = ps;


    fd.density = 1;
    fd.friction = 0.3;
    fd.restitution = 0.5;

    //create body definition 
    BodyDef bd = new BodyDef();
    bd.type = BodyType.DYNAMIC;
    bd.position.set(box2d.coordPixelsToWorld(center));

    body = box2d.createBody(bd);
    body.createFixture(fd);

    //body.setLinearVelocity(new Vec2(random(-5,5), random(2,5)));
    //body.setAngularVelocity(random(-5,5));
  }
}

JointPair.pde

class JointPair {
  Box b1, b2;

  float len;

  JointPair(float x, float y) {
    len = 50;

    b1 = new Box(x, y);
    b2 = new Box(x+5, y+5);

    DistanceJointDef djd = new DistanceJointDef();
    djd.bodyA = b1.body;
    djd.bodyB = b2.body;

    djd.length = box2d.scalarPixelsToWorld(len);

    djd.frequencyHz = 3; 
    djd.dampingRatio = 0.1;

    DistanceJoint dj = (DistanceJoint) box2d.world.createJoint(djd);
  }

  void display(){
    Vec2 box1 = box2d.getBodyPixelCoord(b1.body);
    Vec2 box2 = box2d.getBodyPixelCoord(b2.body);
    
    stroke(0);
    strokeWeight(2);
    line(box1.x,box1.y,box2.x,box2.y);
    
    b1.display();
    b2.display();
    
  }
  
  boolean isPairOffScreen(){
    if(b1.isOffScreen() && b2.isOffScreen()){
      b1.killBody();
      b2.killBody();
      return true;
    }else{
      return false;
    }
  }
}

[opheliagame]

I've been getting this error too. I think you're trying to destroy bodies as well and that's when the error occurs. Have you been able to find a solution yet?

[EmpresarioDelCircoPalace]

Well, I have the same error, I'm killing bodys too.... Did any of you find a solution?

Would be lovely to hear it