Thread: NullPointerException when comparing string in binary tree

HI there, please help out with a bug i encountered during my binary tree assignment.

i searched the net for a binary tree code and thanks to CHINMAY LOKESH, i found one with a tree displays in it. i altered the code a bit to compare "string" rather than "integer". tree displaying, Inserting, deleting, and finding was doing fine when i encounter a bug when finding a value that is not inside the tree. the description are as follows...

this is the number i entered into the tree.

das
dd
5g
3213
ds6
asd
o56o
hj23
0ghj
asd
1

the Binary Tree was Created Successfully! i check the displays of the tree.

when i find the number "2"
it was doing what it supposed to by saying cannot find the number "2"

but when i try to find the number "22"
nothing occurs and this error message was displayed...

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at Tree.find(Tree.java:14)

this is the code in the applet...

public Node find(String val)
    {
            Node current = root;
line 14:  while(val.equals(current.item) == false)
            {
            if(val.length()>current.item.length())
            {
            	current = current.rightChild;
            }
            else if(val.length()<current.item.length())
            {
            	current = current.leftChild;
            }
            else
            {
            	if(val.compareToIgnoreCase(current.item)<0)
            		current = current.leftChild;
            	else
            		current = current.rightChild;
            	if(current == null)
                return null;
            }
        }
        return current;
    }

the odd thing is.... the value i use for finding in the range of 10 till 59 gave the same errors, but finding for 9 or 60 displays cannot find which is correct by the way...

another thing i noticed which is also weird...

if i did the find method for 10 till 60 after i inserted a number of "30"
the programs work fine and gave a message that those numbers cannot be found...

??? i have no ideas what's happened... any ideas from the community here?

this my first time posting a thread here, if you need extra info do pm here.
thanks in advance and have a nice day.

ps. tetkun.

Thanks for your suggestion norm... i figure it out by doing a bit searching on the error message on the net. it seems that though the first value (val & current.item) was not null, which in case made me puzzled why the heck presented the null errors, the last value (current.item) when it search down the tree would eventually came to a null while looping down the tree. i fix it by changing the while statement with (while current != null) and use an if statement for the condition (if (val.equalsIgnoreCase.(current.item))) inside the while loop. then use "break" to end the looping when the value was found. thanks for pointed me out to look for the null value that occurs... pulled out few hairs while thinking about it but i'm glad that my tree is finally bug free... thank you and have a nice day.