how to make , that when mob is walking, and when he walks on lava he places water, to put it out

Overriding handleLavaMovement seems like a good place to start.

 

The method name is misleading, sorry. After looking through Entity code, I think it'd be better to just put it in the onEntityUpdate method.

 

E.g.

 

public void onEntityUpdate()
{
    if(this.handleLavaMovement())
    {
        //DO STUFF
    }
    super.onEntityUpdate();
}