Structural Pattern Matching in Java

This article made me realize the relationship between structural pattern matching and polymorphism. How I would solve the problem in C++ (with constructors and error checking omitted for brevity):

  class Tree {
  public:
    virtual int depth() = 0;
  };

  class Empty: public Tree {
  public:
    virtual int depth() { return 0; }
  };

  class Leaf: public Tree {
    int n;
  public:
    virtual int depth() { return 1; }
  };

  class Node: public Tree {
    Tree* l;
    Tree* r;
  public:
    virtual int depth()
    {
      return 1 + max(l->depth(), r->depth());
    }
  };

Since I've never programmed in a language with structural pattern matching, I welcome others to compare my solution to what was presented. Clearly, structural pattern matching requires less code. Also, I've never actually read the Design Patterns book, but I think what I have above is different from the Interpreter and Visitor pattern he described in the article - for one, I don't have any mutation. But, again, please correct me if I'm wrong.