Question

Note: Once completed, run BXTDriver.class, then record the output to result.txt under your assignment folder. Without result.txt, you will receive zero(0) for this assignment.

For this assignment, we will build a binary expression tree, display it, and evaluate it.   This time, we will encapsulate the behavior in a BXT class.   The driver class, tree node, as well as the BXT class are provided. Please implement appropriate methods in BXT class to build, display and evaluate a tree. 

Let's also allow decimal input and output, and negative numbers.  For simplicity, all tokens in the input string be separated by a space.

Sample run

Postfix Exp: 14 -5 / BXT: -5 / 14 Infix order: 14 / -5 Prefix order: / 14 -5 Evaluates to -2.8 ------------------------

Postfix Exp: 20 3 -4 + * BXT: -4 + 3 * 20 Infix order: 20 * 3 + -4 Prefix order: * 20 + 3 -4 Evaluates to -20.0 ------------------------

Postfix Exp: 2 3 + 5 / 4 5 - * BXT: 5 - 4 * 5 / 3 + 2 Infix order: 2 + 3 / 5 * 4 - 5 Prefix order: * / + 2 3 5 - 4 5 Evaluates to -1.0 ------------------------

Build a BXT You need to change the string into a tree. Hint1: In a postfix string the operator is preceded by two operands (numbers). This suggests a stack of TreeNodes would be useful. Hint 2: Each operator is a TreeNode with two children. Hint 3: If the token is an operator, do what? Else it's a number, so do what? Display Infix and Prefix orders Infix is characterized by the placement of operators between operands; Prefix expression notation requires that all operators precede the two operands that they work on; Postfix requires that its operators come after the corresponding operands. See following examples: Infix Expression Prefix Expression Postfix Expression A + B + A B A B + A + B * C + A * B C A B C * + Evaluating the Expression Do this recursively. If the node is an operator, recursively evaluate the left child and the right child, and return the result. Else the node is a number, so it can be converted into a double, and returned. Want to do more? (Optional) Print the infix order with parenthese

/** INSTRUCTION
* Create a class named BXT.java the copy and past the content
* Once completed, please record how long time you spent on this assignment
* and list all resources you have used to complete this assignment.
*/
import java.util.*;
  
/*******************
Represents a binary expression tree.
The BXT can build itself from a postorder expression. It can
evaluate and print itself. It also prints an infix string, a prefix string and a postfix.
**********************/
class BXT{
private int count; //will be used in another assignment if we have time
private TreeNode root;
public BXT(){
count = 0;
root = null;
}
public void buildTree(String str){
//TO DO
}
public double evaluateTree(){
//To DO
}

public String display(){
//TO DO
}

public String infix(){
//TO DO
}

public String prefix(){
//TO DO
}

public String postfix(){
//TO DO
}

}

Answer 1

Program Screenshot:

BXT.java