Please can someone help me with this code. postfixToprefix output is not corrct when I compile the code. It display the operand and no operator. here is the code.

package gui;

import java.util.Stack;

class prefixToPostFix {

private static String prefixToPostfixConversion(String prefixExp) {

final String LEFT_DONE = "LEFTDONE";

Stack operatorStack = new Stack<>();

StringBuilder strPostfix = new StringBuilder();

if (prefixExp.trim().isEmpty()) {

return null;

}

char[] chars = prefixExp.toCharArray();

for (char aChar : chars) {

if (isOperator(aChar)) {

operatorStack.push(String.valueOf(aChar));

//System.out.println("aChar = " + aChar);

} else {

System.out.println("h");

strPostfix.append(String.valueOf(aChar));

while (!operatorStack.empty() && !operatorStack.peek().equals(LEFT_DONE)) {

String c=operatorStack.pop();

System.out.println("c = " + c);

strPostfix.append(c);

}

operatorStack.push("LEFTDONE");

}

}

return strPostfix.toString();

}

private static boolean isOperator(char c) {

char[] operators = { '+', '-', '/', '*'};

boolean isOp = false;

for (char operator : operators) {

if (c == operator) {

isOp = true;

break;

}

}

return isOp;

}

public String look(String calculation) {

return prefixToPostfixConversion(calculation);

}

}

class postFixToPrefix {

//function to check if character is operator or not

public boolean isOperator1(char x) {

switch (x) {

case '+':

case '-':

case '/':

case '*':

return true;

}

return false;

}

// convert postfix to prefix expression

public String postfixToPrefix(String post_exp) {

Stack s = new Stack() ;

//length of expression

int length = post_exp.length();

// reading from right to left

for (int i = 0; i < length; i++) {

// check if symbol is operator

if (isOperator1(post_exp.charAt(i))) {

//pop two operands from stack

String op1 = s.peek();

s.pop();

String op2 = s.peek();

s.pop();

//concat the operands and operator

String temp = post_exp.charAt(i) + op2 + op1;

//push string temp back to stack

s.push(temp);

}

// if symbol is an operand

else {

//push the operand to the stack

s.push(String.valueOf(post_exp.charAt(i)));

}

}

// stack[0] contains the prefix expression

return s.peek();

}

//Driver Code

public String look(String calculation) {

return postfixToPrefix(calculation);

}

}

class DivideByZero extends Exception {

// A constructor that reads the message

DivideByZero(String message) {

super(message);

}

}

class InvalidCharacterException extends Exception {

// Constructor

InvalidCharacterException() {

}

}