// Source code example for "A Practical Introduction
// to Data Structures and Algorithm Analysis"
// by Clifford A. Shaffer, Prentice Hall, 1998.
// Copyright 1998 by Clifford A. Shaffer

import java.io.*;

// Leaf and internal node classes for variable node
//   implementation of BinNode.
// The implementation is for an expression tree.
// The internal nodes store a single character for an
//   operator, and two child pointers.
// The leaf nodes store a string for an operand.

class LeafNode implements BinNode { // Leaf node subclass
  private String var;               // Operand value

  public LeafNode(String val) { var = val; } // Constructor
  public Object element() { return var; }
  public Object setElement(Object v) { return var = (String)v; }
  public BinNode left() { return null; }
  public BinNode setLeft(BinNode p) { return null; }
  public BinNode right() { return null; }
  public BinNode setRight(BinNode p) { return null; }
  public boolean isLeaf() { return true; }
} // class LeafNode

class IntlNode implements BinNode { // Internal node subclass
  private BinNode left;             // Left child
  private BinNode right;            // Right child
  private Character opx;            // Operator value

  public IntlNode(Character op, BinNode l, BinNode r)
    { opx = op; left = l; right = r; } // Constructor
  public Object element() { return opx; }
  public Object setElement(Object v) { return opx = (Character)v; }
  public BinNode left() { return left; }
  public BinNode setLeft(BinNode p) { return left = p; }
  public BinNode right() { return right; }
  public BinNode setRight(BinNode p) { return right = p; }
  public boolean isLeaf() { return false; }
} // class IntlNode

// Driver class for variable BinNode implementation
class VarMain {

static void VisitLeafNode(Object val) {
  System.out.println("Leaf: " + val);
}

static void VisitInternalNode(Object val) {
  System.out.println("Internal: " + val);
}

// Traverse a binary tree implemented with variable
//   BinNode implementation
static void traverse(BinNode rt) { // Preorder traversal
  if (rt == null) return;          // Nothing to visit
  if (rt.isLeaf())                 // Process leaf node
    VisitLeafNode(rt.element());
  else {                           // Processinternal node
    VisitInternalNode(rt.element());
    traverse(rt.left());
    traverse(rt.right());
  }
}

  // Main routine for variable BinNode test
  public static void main(String args[]) throws IOException {
    BinNode temp1, temp2, root;
    String string1 = "Hello1";
    String string2 = "Another string";

    temp1 = new LeafNode(string1);
    temp2 = new LeafNode(string2);
    root = new IntlNode(new Character('+'), temp1, temp2);
    traverse(root);
    System.in.read();
  }
}