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Thread: Creating new instance

  1. #1
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    Default Creating new instance

    Hello JPF. I am currently working on a program that builds an expression tree. I am provided with class BinaryTree and I am having trouble constructing a new node.

    1) This works:
    BinaryTree<String> newTree = new BinaryTree<String>(nextToken,null,null);

    2) This doesn't work:
    BinaryTree<String> newTree = new Node(nextToken);

    I'm trying to get number 2 to work. Can someone please help me out and explain why it doesn't work?

    This is the BinaryTree class:
    import java.io.*;
     
    /** Class for a binary tree that stores type E objects.
    *   @author Koffman and Wolfgang
    * */
     
    public class BinaryTree < E > implements Serializable 
    {
     
      /** Class to encapsulate a tree node. */
      protected static class Node < E >
          implements Serializable {
        // Data Fields
        /** The information stored in this node. */
        protected E data;
     
        /** Reference to the left child. */
        protected Node < E > left;
     
        /** Reference to the right child. */
        protected Node < E > right;
     
        // Constructors
        /** Construct a node with given data and no children.
            @param data The data to store in this node
         */
        public Node(E data) 
        {
          this.data = data;
          left = null;
          right = null;
        }
     
        // Methods
        /** Return a string representation of the node.
            @return A string representation of the data fields
         */
        public String toString() {
          return data.toString();
        }
      }
     
      // Data Field
      /** The root of the binary tree */
      protected Node < E > root;
     
      public BinaryTree() {
        root = null;
      }
     
      protected BinaryTree(Node < E > root) {
        this.root = root;
      }
     
      /** Constructs a new binary tree with data in its root,leftTree
          as its left subtree and rightTree as its right subtree.
       */
      public BinaryTree(E data, BinaryTree < E > leftTree,
                        BinaryTree < E > rightTree) {
        root = new Node < E > (data);
        if (leftTree != null) {
          root.left = leftTree.root;
        }
        else {
          root.left = null;
        }
        if (rightTree != null) {
          root.right = rightTree.root;
        }
        else {
          root.right = null;
        }
      }
     
      /** Return the left subtree.
          @return The left subtree or null if either the root or
          the left subtree is null
       */
      public BinaryTree < E > getLeftSubtree() {
        if (root != null && root.left != null) {
          return new BinaryTree < E > (root.left);
        }
        else {
          return null;
        }
      }
     
      /** Return the right sub-tree
            @return the right sub-tree or
            null if either the root or the
            right subtree is null.
        */
        public BinaryTree<E> getRightSubtree() {
            if (root != null && root.right != null) {
                return new BinaryTree<E>(root.right);
            } else {
                return null;
            }
        }
     
     
    /**** EXERCISE ****/
     
      /** Determine whether this tree is a leaf.
          @return true if the root has no children
       */
      public boolean isLeaf() {
        return (root.left == null && root.right == null);
      }
     
      public String toString() {
        StringBuilder sb = new StringBuilder();
        preOrderTraverse(root, 1, sb);
        return sb.toString();
      }
     
      /** Perform a preorder traversal.
          @param node The local root
          @param depth The depth
          @param sb The string buffer to save the output
       */
      private void preOrderTraverse(Node < E > node, int depth,
                                    StringBuilder sb) {
        for (int i = 1; i < depth; i++) {
          sb.append("  ");
        }
        if (node == null) {
          sb.append("null\n");
        }
        else {
          sb.append(node.toString());
          sb.append("\n");
          preOrderTraverse(node.left, depth + 1, sb);
          preOrderTraverse(node.right, depth + 1, sb);
        }
      }
     
      /** Method to read a binary tree.
          pre: The input consists of a preorder traversal
               of the binary tree. The line "null" indicates a null tree.
          @param bR The input file
          @return The binary tree
          @throws IOException If there is an input error
       */
      public static BinaryTree < String >
          readBinaryTree(BufferedReader bR) throws IOException {
        // Read a line and trim leading and trailing spaces.
        String data = bR.readLine().trim();
        if (data.equals("null")) {
          return null;
        }
        else {
          BinaryTree < String > leftTree = readBinaryTree(bR);
          BinaryTree < String > rightTree = readBinaryTree(bR);
          return new BinaryTree < String > (data, leftTree, rightTree);
        }
      }
     
    }


  2. #2
    Super Moderator helloworld922's Avatar
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    Default Re: Creating new instance

    Are you trying to call the second constructor from an external class? Cause that constructor was declared protected. Other than that, there's not much difference as far as I can tell. If you want to make it easier to maintain, make that method like this:

    public BinaryTree(Node<E> root)
    {
         BinaryTree(root,null,null);
    }

  3. The Following User Says Thank You to helloworld922 For This Useful Post:

    vluong (November 28th, 2009)

  4. #3
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    Default Re: Creating new instance

    I'll give that a try!

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