Hi guys,

I'm trying to implement a work with Box2D. And in order to implement collision detection, as far as i could search on web, I have to create a class that extends ContactListener.

The problem is that Processing is complaining that ContactListener must be a class. And after exploring the Box2D's docs, I saw that ContactListener is, in fact, a 'interface' not a class.

Ok... that explains why Processign was complaining. But... do not solve my problem...

Well, I'm not a Java guru, but I tried do do some thing:

Code:

class MyCollisions implements ContactListener{

  ArrayList contacts;
  
  MyCollisions(){
  }
  
  void persist(ContactPoint point){
    println("Persist Contact");
  }
    
  void Add(ContactPoint point){
    println("COLLISION ----------------------------------");
    println("shape1: "+point.shape1);
    println("shape2: "+point.shape2);
    println("separation: "+point.separation);
    println("position: "+point.position);
  }
  

  void remove(ContactPoint point){
    println("Remove Contact");
  }
  
  void result(ContactPoint point){
    println("Result Contact");
  }
}
 

Ok... now Processing seems to be ok with the 'implements' task.
But now... a new problem!

Processing complains:
Code:

The type box_00.Colisoes must implement the inherited abstract method ContactListener.persist(ContactPoint) 

now... i am stuck! As you can see... I do implement all the methods from ContactListener interface. Unless there is some secret way to implement sucha methods, diferent from what i did.

Does anyone knows how can I implement a java interface?

thanks in advance,
Paulo
P.S.: down here is the ContactListener code:
Code:

/*
 * JBox2D - A Java Port of Erin Catto's Box2D
[...] */

package org.jbox2d.dynamics;

import org.jbox2d.dynamics.contacts.ContactPoint;
import org.jbox2d.dynamics.contacts.ContactResult;

public interface ContactListener {

		/**
		 * Called when a contact point is added. This includes the geometry
		 * and the forces.
		 */
		public void add(ContactPoint point);

		/**
		 * Called when a contact point persists. This includes the geometry
		 * and the forces.
		 */
		public void persist(ContactPoint point);

		/**
		 * Called when a contact point is removed. This includes the last
		 * computed geometry and forces.
		 */
		public void remove(ContactPoint point);
		
		public void result(ContactResult point);

}

 

You are implementing it the right way. There is a mistake, though :
result(ContactResult r)

Code:

class MyCollisions implements ContactListener {

  ArrayList contacts;
  
  MyCollisions() {}
  
  void add(ContactPoint p) {}
  void result(ContactResult r) {}
  void remove(ContactPoint p) {}
  void persist(ContactPoint p) {}  
  
}