Question

Write a program that converts prefix expressions to postfix and postfix expressions to prefix. (java)

The program for this project should consist of three classes.

-The main class should create a GUI that allows the user to input an expression in either prefix or postfix and convert it to postfix or prefix, respectively.

-The other class should contain the code to perform the conversions.

--->The pseudocode for prefix to postfix, which requires two stacks, is shown below:

tokenize the string containing the prefix expression

while there are more tokens

push the token onto a reversal stack if it is not a space

while the reversal stack is not empty

pop the next token from the reversal stack

if it is an operand

push it onto the operand stack

else it is an operator

pop two operands off of the operand stack

create a string with the two operands followed

the operator

push that string onto the operand stack

pop the postfix expression off the stack

The pseudocode for the postfix to prefix conversion, which requires only one stack, is shown below:

tokenize the string containing the postfix expression

while there are more tokens

get the next token

if it is a space

skip it

else if it is an operand

push it onto the operand stack

else it is an operator

pop two operands off of the operand stack

create a string with the operator followed by

two operands

push that string onto the operand stack

pop the prefix expression off the stack

A checked exception SyntaxError should be thrown by the methods that perform the conversions if an empty stack is ever popped or the stack is not empty once the conversion is complete. That exception should be caught in the main class, where a JOptionPane window should be displayed containing an error message.

Answer 1

PROGRAM

import javax.swing.JOptionPane;
import java.util.Stack;
public class postfixprefix {
        
        static boolean Operator(char x){
        switch (x){
            case '-':
            case '+':
            case '/':
            case '*':
            case '^':
                return true;
        }
        return false;
    }
        
        public static String convert_Prifix(String expression){

        Stack<String> stack = new Stack<>();
        for (int i = 0; i <expression.length() ; i++) {

            char c = expression.charAt(i);

            if(Operator(c)){
                String s1 = stack.pop();
                String s2 = stack.pop();
                String temp = c + s2 + s1;
                stack.push(temp);
            }else{
                stack.push(c+"");
            }
        }
        String result = stack.pop();
        return result;
    }
         public static String convert_Postfix(String expression){

                Stack<String> stack = new Stack<String>();
                for (int i = expression.length()-1; i >=0 ; i--) {

                    char c = expression.charAt(i);

                    if(Operator(c)){
                        String s1 = stack.pop();
                        String s2 = stack.pop();
                        String temp = s1 + s2 + c;
                        stack.push(temp);
                    }else{
                        stack.push(c+"");
                    }
                }

                String result = stack.pop();
                return result;
            }

        public static void main(String[] args) {
                                String postfix,prefix,input,expression;
                                int n;
                                expression = JOptionPane.showInputDialog("Enter Expression");
                                input= JOptionPane.showInputDialog("Enter 1 for prefix and 2 for postfix");
                                n = Integer.parseInt(input);
                                if(n==1) {
                                        prefix= convert_Prifix(expression);
                                    JOptionPane.showMessageDialog(null,"Prefix Expression: "+ prefix);
                                }
                                else {
                                        postfix= convert_Postfix(expression);
                                    JOptionPane.showMessageDialog(null,"Postfix Expression: "+ postfix);
                                }
                                
        }

}

OUTPUT