Please help for a LinkBinaryTreeInJava

I am new in this group,I don't know how far it would help me.
I tried to make a linked based binary tree following the book "data
structures and algorithms in java" By goodRich and tamassia.I did all
but I wanted to implement a function to determine whether a particular
node exists or not.All I want to implement a function boolean
exists(node n).Can anyone help??My program is as follows:-

import java.io.*;

interface Node {
        Object getData();
        int getID();
               }

class TreeEmptyException extends Exception {
      TreeEmptyException(String message) {
      super(message);
    }
}

class LinkBinTree {
      BinNode root;
      int size;
      LinkBinTree(Object O) {
          root = new BinNode(0);
                            }

class BinNode implements Node {
            int id;
            BinNode left;
            BinNode right;
            Object data;
       BinNode(int iden) {
            id = iden;
            left = null;
            right = null;
            data = null;
                         }
       BinNode(Object O) {
            id = 0;
            left = null;
            right = null;
            data = null;
                        }
       public Object getData() {return data;}
       public int getID() { return id;}

        void addLeft(Object obj) {
             BinNode b = new BinNode(obj);
             left = b;
                                  }

        void addRight(Object obj) {
             BinNode r = new BinNode(obj);
             right = r;
                                  }

      BinNode addLeft(Node n,Object O) throws TreeEmptyException
    {
             if(!exists(n)) throw new TreeEmptyException("Tree doesn't
exists");
             return n.addLeft(O);
}

      BinNode addRight(Node n,Object O) throws TreeEmptyException{
    if(!exists(n)) throw new TreeEmptyException("Tree doesn't
exists");
            return n.addRight(O);
}

      void preOrder(Node n) {
              LinkQueueApp<Integer> q =new LinkQueueApp<Integer>();
              int p=n.getID();
              q.enqueue(p);
              while(!q.isEmpty()) {
                    p =q.dequeue();
                    System.out.println("The pre-order is : "
+n.getData());
                    for(int i=p;(i==p+1) || (i==p+2)&&i<=size;i++)
                        q.enqueue(i);
                                  }

}

 void boolean exists(Node n) {
         if(Node == root) return;
         else {
            if(Node