Error message doesn't display correctly

I'm trying to make dialog that will display an error message whenever I make wrong move in my scrabble game. So in Problem.java, I make it like this

class Problem
{
   Problem(String s)
  {
        message = s;
  }
}

So I write code to display the warning like this :

    void displayProblem(Problem p)
    {

        JOptionPane.showMessageDialog(this,p, "WARNING!",JOptionPane.WARNING_MESSAGE);
    }

I expect error message when I don't put tile something like this : "no tiles placed" just like what's in the code but it ended up like this :

What's wrong with my code anyway?

You either need to pass p.message to the dialog or override Problem's toString() method and return message there. What you're seeing is the output of standard toString(), i.e. class name + instance id.