Question

Return a method as an expression tree

Hi guys.

I need to return a method as an expression tree, it's currently returning null.

public static ExpressionTree getExpressionTree(String expression)
throws Exception {      
char[] charArray = expression.toCharArray();
Node root = et.constructTree(charArray);
System.out.println("infix expression is");
et.inorder(root);
return et;
}

In the above method, et needs to have a value. -- Take a look at the complete class below.

; public class ExpressionTree extends BinaryTree { private static final String DELIMITERS = " +-*/() // A utility function to check if c' // is an operator static boolean isOperator (char c) { if (c == "+' IIC == - II C == *** II C == '/' Il c == "") { return true; return false; // Utility function to do inorder traversal static void inorder (Node t) { if (t != null) { inorder (t.left); System.out.print (t.value + " "); inorder (t.right); // Returns root of constructed tree for given // postfix expression static Node constructTree (char postfix[]) { Stack<Node> st = new Stack(); Node t, ti, t2; // Traverse through every character of // input expression for (int i = 0; i < postfix.length; i++) { // If operand, simply push into stack if (!isOperator (postfix[i])) { t = new Node (postfix[i]); st.push(t); } else // operator

Kindly assist.

Answer 1

First of All, the "Node" class is missing, you should add Node class then only you can access the object of the node.

A node class is given below and the properties and Constructor is given below.

So now you can access the Node object and you can return the expression tree without any exception.

//Code start Here

import java.util.Stack;
// You need to add this class Node to your script
// your accessing Node object without node class
// so it throws exception
class Node {

    char value;
    Node left, right;

    Node(char item) {
        value = item;
        left = right = null;
    }
}

/* The real ExpressionTree is started here
write your code for expression tree

Node constructTree(char postfix[]) { 
..
..
..
return t;
*/

//Also add main function in your code this will increase the chance to return your expecting //Expression Tree
  
  public static void main(String args[]) {

        ExpressionTree et = new ExpressionTree();
        String postfix = "ab+ef*g*-";
        char[] charArray = postfix.toCharArray();
        Node root = et.constructTree(charArray);
        System.out.println("infix expression is");
        et.inorder(root);

    }
}

// This code has been contributed by Mayank Jaiswal

//Code ends here

Other than this every code in this file is correct. What you want to do is just Add the Node class to your script...

Thank you