Question

insertion

Asked by: compscigirl

hi, i'm doing a BinarySearchTree program and i'm having a problem with the insertion method.
the pseudocode for insertion was
     *void insert (TreeNode node, Object data)
            // Will insert data into an ordered binary tree.
            // The solution is recursive.
            {
               if
                  node points to null, insert data as a new TreeNode pointed to by node
               else
                  if (data < node.getValue())
                     recursively insert data to the left
                  else if (data > node.getValue())
                     recursively insert data to the right
            }



my implementation:


    private void insert(TreeNode node, Object data)
    {
            if (node == null)
                  node.setValue(new TreeNode(data, null, null));
            else
            {
                  if (((Item)data).compareTo((Item)node.getValue()) < 0)
                      insert(node.getLeft(), data);
                  else
                        insert(node.getRight(), data);
            }
      }

i know that this code gives me NullPointerException since i can't setValue on a null node
but how else am i going to insert data into null nodes??

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Asked On
2004-03-17 at 15:41:20ID20922639
Tags

method

Topic

Java Programming Language

Participating Experts
2
Points
20
Comments
11

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Answers

 

by: greenlantern0Posted on 2004-03-17 at 16:03:09ID: 10619858

private TreeNode root = null;

private void insert(TreeNode node, Object data) {

        if (root == null)              
               root = node;
               
          else
          {
               if (((Item)data).compareTo((Item)node.getValue()) < 0)
                   insert(node.getLeft(), data);
               else
                    insert(node.getRight(), data);
          }
 }

maybe this will help...

 

by: greenlantern0Posted on 2004-03-17 at 16:34:55ID: 10620003

private void insert(TreeNode node, Object data)
    {
         
         if (((Item)data).compareTo((Item)node.getValue()) < 0) {
               
                       if(node.getLeft() == null)
                             node.setLeft(new TreeNode(data, null, null));
                       else
                         insert(node.getLeft(), data);
                }
                   
               else {
                       if(node.getRight() == null)
                          node.setRight(new TreeNode(data, null, null));
                       else
                          insert(node.getRight(), data);
                 }
          }
     }

or this...

 

by: compscigirlPosted on 2004-03-17 at 19:11:13ID: 10620620

hi greenlantern0,
i tried both. the first one doesn't seem to insert anything. when i printed out the list, it's blank. The second one gives:


Binary Search Tree Menu

(1) Load file
(2) In order print
(3) Pre order print
(4) Post order print
(5) Search
(6) Delete
(7) Count nodes
(Q) Quit

Choice ---> 1

Please enter the name of the file you want to make a tree ---> file20
Exception in thread "main" java.lang.NullPointerException
        at BSTree.insert(BSTree.java:63)    <- error.
        at BSTree.loadFile(BSTree.java:42)
        at BSTree.sortMenu(BSTree.java:206)
        at BSTree.main(BSTree.java:267)
Press any key to continue...


 

by: greenlantern0Posted on 2004-03-17 at 20:29:26ID: 10620986

private void insert(TreeNode node, Object data)
    {
          if (node == null)
          node = new TreeNode(data, null, null);
         
         if (((Item)data).compareTo((Item)node.getValue()) < 0) {
               
                      if(node.getLeft() == null)
                           node.setLeft(new TreeNode(data, null, null));
                      else
                        insert(node.getLeft(), data);
                }
                   
               else {
                      if(node.getRight() == null)
                       node.setRight(new TreeNode(data, null, null));
                      else
                         insert(node.getRight(), data);
                 }
          }
     }

Where is line 63 in the insert method? How are you calling the insert method? Are you putting print statements in your code so you can see when in the traversing of the tree the Nullpointer is showing up? I am assuming that it's at the very start of forming the tree.. but just want to be sure.

 

by: greenlantern0Posted on 2004-03-17 at 20:30:41ID: 10620988

the second if statement should be an else if

sorry

 

by: compscigirlPosted on 2004-03-17 at 20:43:52ID: 10621043

hi,
i did
                Object data = new Item(id, inv);
                  insert(root, data);

 

by: mayankeaglePosted on 2004-03-17 at 22:04:26ID: 10621342

What seems to be the problem now?

 

by: compscigirlPosted on 2004-03-18 at 18:11:33ID: 10629865

hi, just that i didn't know how to fix my code- the one i couldn't use null to getValue();

 

by: mayankeaglePosted on 2004-03-18 at 20:17:48ID: 10630334

Can you post your updated code?

 

by: compscigirlPosted on 2004-03-19 at 22:34:42ID: 10639239

it's ok i solved it

 

by: compscigirlPosted on 2004-03-19 at 22:38:26ID: 10639251

thnx guys

20120131-EE-VQP-002

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