Processing example of event dispatching.

ExampleDispatcher.pde

class ExampleDispatcher {
  private Object _listener;
  
  public void setListener(Object obj) {
    _listener = obj;
  }
  
  public void dispatchBasic() {
    try {
      Method callback = _listener.getClass().getMethod("handleBasicEvent");
      callback.invoke(_listener); // calls the method with itself as the scope. _listener should always be the first argument.
    }
    catch(Exception e) {
      // the listener probably doesn't have void basicEventHandler();
    }
  }
  
  public void dispatchWithArguments() {
    try {
      // in order to find the correct method we have to specify that we're looking for a method named "handleEventWithArgs"
      // that accepts two arguments: one of type int, one of type float. here's how we do that.
      Method callback = _listener.getClass().getMethod("handleEventWithArgs",int.class,float.class);
      
      // we know our listener must be the first argument from our basic example.
      callback.invoke(_listener,1,3.14); 
    }
    catch(Exception e) {}    
  }
  
  public void dispatchAddOneToNumber() {
    try {
      Method callback = _listener.getClass().getMethod("addOne",int.class);
      Object invokedResult = callback.invoke(_listener,1); // always returns type Object. We can cast from there.
      int total = (int) invokedResult;

      println("The total is :: " + total);
    }
    catch(Exception e) {
      
    }
  }
};

sketch.pde

ExampleDispatcher myDispatcher;

void setup() {
  myDispatcher = new ExampleDispatcher();
  myDispatcher.setListener(this);
  
  myDispatcher.dispatchBasic();
  myDispatcher.dispatchWithArguments();
  myDispatcher.dispatchAddOneToNumber();
}

// a basic simple event.
void handleBasicEvent() {
  println("A basic event!");
}

// arguments will get passed from myDispatcher.
void handleEventWithArgs(int arg1,float arg2) {
  println("arg1 is :: " + arg1 + " and arg2 is" + arg2);
}

// an example of communicating between the two.
int addOne(int num) {
  return num+1;
}