here is the here is background information.

the todo part

1 package expressiontree; 2 3 import java.util.Stack; 4 5 public class ExpressionTree i private Node root; private String postfix; 7 10e public class Node i 12 13 14 15e 16 17 18 19 20 21 Node left, right; String data; private Node(String s)i data-S; left-null; right-null; 23 24 25e 26 27 28 29 30 31 32 /* Initialize the tree, assign parameter, and generate the ExpressionTree * based on the postfix string. */ public ExpressionTree(String postfix) 5 root - null; this.postfix-postfix; generateTreeFromPostFixO; public Node getRoot) i return root; 34