Binary Tree

[vcm]

Hi guys, Im complete lost as to how to create a static Binary Tree object.

My assignment states that I have to "Write a static method named ex1() that returns a BinaryTree object representing the expression (2 + 4) * 8"

here is the code i have so far

BinaryTree.java

import java.io.*;

/** Class for a binary tree that stores type E objects.
*   @author Koffman and Wolfgang
* */

public class BinaryTree < E >
    implements Serializable {
	
	private static final long serialVersionUID = 1L;
	


  // 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);
    }
  }
  
  public static BinaryTree ex1(){
	return null;
  }
  
  public static BinaryTree ex2(){
	  return null;
	  
  }
}

Node.java ( i removed the node class from binary tree because that is what my teacher wanted me to do "The book defines the Node class within the Binarytree class. Move the Node class into its own public definition inside Node.java. Add/remove import statements as needed."
did i do it the right way?

import java.io.*;

import BinaryTree.Node;



/** Class to encapsulate a tree node. */
class Node < E >
    implements Serializable {
	
	private static final long serialVersionUID = 1L;
	
  // 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();
    }
  }

so my two questions are, did i create the Node.java correctly

and how do i create the BinaryTree object called ex1() that returns the statement (2+4)*8

Thank You