// This class represents a tree of integers
public class IntTree {
   private IntTreeNode overallRoot;
   
   // Constructs an empty tree.
   public IntTree() {
      overallRoot = null;
   }
   
   // Prints the numbers in this tree in a pre-order fashion.
   public void printPreorder() {
      System.out.print("preorder:");
      printPreorder(overallRoot);
      System.out.println();
   }
   
   // Prints the numbers of the subtree rooted at root
   // using a pre-order traversal.
   private void printPreorder(IntTreeNode root) {
      if (root != null) {
         System.out.print(" " + root.data);
         printPreorder(root.left);
         printPreorder(root.right);
      }
   }
   
   // Prints the numbers in this tree in a in-order fashion.
   public void printInorder() {
      printInorder(overallRoot);
   }
   
   // Prints the numbers of the subtree rooted at root
   // using a in-order traversal.
   private void printInorder(IntTreeNode root) {
      if (root != null) {
         printInorder(root.left);
         System.out.print(" " + root.data);
         printInorder(root.right);
      }
   }
   
   // Prints the numbers in this tree in a post-order fashion.
   public void printPostorder() {
      printPostorder(overallRoot);
   }
   
   // Prints the numbers of the subtree rooted at root
   // using a post-order traversal.
   private void printPostorder(IntTreeNode root) {
      if (root != null) {
         printPostorder(root.left);
         System.out.print(" " + root.data);
         printPostorder(root.right);
      }
   }
   
   
   // Class that represents a single node in the tree
   private static class IntTreeNode {
      public int data;
      public IntTreeNode left;
      public IntTreeNode right;
      
      // Constructs a leaf node with given data
      public IntTreeNode(int data) {
         this(data, null, null);
      }
      
      // Constructs a branch node with given data, left subtree, right subtree
      public IntTreeNode(int data, IntTreeNode left, IntTreeNode right) {
         this.data = data;
         this.left = left;
         this.right = right;
      }
   }
}