interface BinTreeVisitor {
  public int forLeaf(Leaf host);
  public int forNode(Node host);
}

abstract class BinTree {
  static BinTreeVisitor sum = new BinTreeVisitor() { /* ANONYMOUS CLASS */
      public int forLeaf(Leaf host) { return host.value; }
      public int forNode(Node host) { return host.left.apply(this) + host.right.apply(this); }
      };
  static BinTreeVisitor max = new BinTreeVisitor() { /* ANONYMOUS CLASS */
      public int forLeaf(Leaf host) { return host.value; }
      public int forNode(Node host) { 
        int leftmax = host.left.apply(this);
	int rightmax = host.right.apply(this);
	return (leftmax > rightmax) ? leftmax : rightmax;
      }};

  abstract int apply(BinTreeVisitor v);

  public static void main(String[] args) {
    System.out.println("Input: " + Node.n3 + " sum = " + Node.n3.apply(sum) + " max = " +
      Node.n3.apply(max));
    System.out.println("Input: " + Node.n2 + " sum = " + Node.n2.apply(sum) + " max = " +
      Node.n2.apply(max));
  }
}

class Leaf extends BinTree {
  static Leaf l7 = new Leaf(7);
  static Leaf l4 = new Leaf(4);
  static Leaf l3 = new Leaf(3);
  static Leaf l20 = new Leaf(20);

  int value;

  Leaf(int v) { value = v; };
  
  int apply(BinTreeVisitor v) { return v.forLeaf(this); }
  
  public String toString() { return Integer.toString(value); }
}

class Node extends BinTree {

  static Node n1 = new Node(Leaf.l7, Leaf.l3);
  static Node n2 = new Node(Leaf.l4, n1);
  static Node n3 = new Node(n2, new Node(Leaf.l20, n1));

  BinTree left;
  BinTree right;

  Node(BinTree l, BinTree r) {
    left = l;
    right = r;
  }
  
  int apply(BinTreeVisitor v) { return v.forNode(this); }

  public String toString() { return "(" + left.toString() + " " 
				 + right.toString() + ")"; }
}