postfix2infix.java

import java.util.*;
 
class PostfixToInfix
{
 
static boolean isOperand(char ch)
{
  // we check for uppercase and lowercase alphabets.
  if(ch >= 'a' && ch <= 'z') 
   return true;
 
  else if(ch >= 'A' && ch <= 'Z')
   return true;
 
  return false;                 // if not an Operand return false;
}
 
// converts postfix to infix and returns the expression
static String convertToInfix(String postfix)
{
  Stack<String> inFix = new Stack<>();
 
  for (int i = 0; i < postfix.length(); i++)
  {
    char ch = postfix.charAt(i);
 
    if (isOperand(ch))
    {
    // Push operands to stack.    
    inFix.push(ch + "");
    }
 
    // Step 2: Evaluate part of the expression and push it again to stack.
    else
    {
    String op1 = inFix.pop();
 
    String op2 = inFix.pop();
 
    inFix.push("(" + op2 + ch + op1 + ")");
    }
  }
 
  return inFix.pop();
}
 
public static void main(String args[])
{
  String postfix = "ABC-*D/";
  System.out.println("The Postfix Expression is: "+ postfix);
  String result = convertToInfix(postfix);
  System.out.println("The Infix Expression is : "+result);
}
 
}