Traversing a binary tree

Question

Hi
I've written the following code for converting Postfix to Infix,it reads a string then reads it letter by letter ,a stack and a Tree is used,and I want to traverse the last object that has poped from the stack,in the following code I used this line:
System.out.println((Character)(((TreeNode)stack.pop()).data));
but it only prints the root of the tree,I tried to traverse it but I don't have any idea,I did sth like this( for traversing another node):
(TreeNode)stack.pop() = ( (TreeNode)stack.pop() ).data;
System.out.println((Character)(((TreeNode)stack.pop()).data));
but it didn't work.
would you plz help me with it.
Here is the code:
import java.util.Scanner;
public class Test
public static void main( String args[])
Scanner input = new Scanner( System.in );
System.out.printf("Enter your String(in Postfix):\n");
String c = input.nextLine();//read a line of text
Stack stack = new Stack();
int i = 0 ;
while( i < c.length() )
char a = c.charAt( i );
if( Character.isLetterOrDigit (a) )
System.out.printf("\n%c" , a );
stack.push( new TreeNode( a ) );
else if( a == '+' || a == '-' || a == '*' || a == '/' )
TreeNode t = new TreeNode( a );
t.insert( 0 , stack.pop() );
t.insert( 1 , stack.pop() );
stack.push( t );
i++;
(TreeNode)stack.pop() = ( (TreeNode)stack.pop() ).data; //<-----Here is the problem
System.out.println((Character)(((TreeNode)stack.pop()).data));
Thax
Bita

Answer 1

Well, two things. First, you're trying to assign to a method call, which isn't valid. The compiler probably told you this.
Second, you're popping things from the stack more often than you need to (e.g., for printing) so the stack probably won't be in the state you need.
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