Java

properties props = new properties();
            props.put("mail.transport.protocol", "smtps");

import java.util.Stack;
public class infixToPostfix{
    private int index;
    private char ch;
    private char lparenthesis='(';
    private char rparenthesis=')';
    Stack stack=new Stack();
    private String output="";
    public boolean isOperator(char op){
        if(op == '^' || op == '*' ||op == '/' || op == '%' || op == '+' || op == '-')return true;
        else return false;
    }
    public boolean isOperand(char opr){
        if(opr >= 'A' && opr <='Z')return true;
        else if(opr >= 'a' && opr <= 'z')return true;
        else return false;
    }
    public int getPrecedence(char c){
        switch(c){
            case '(': case ')': return 5;
            case '^':return 4;
            case '*': case '/': case '%': return 3;
            case '+': case '-': return 2;
        }return 0;
    }
    public String getPostfix(String expr){      
        stack.push('(');
        for(index=0;index<expr.length();index++){
            ch=expr.charAt(index);                      
            if(isOperand(ch)){
                output=output+ch;
            }
            else if(ch == lparenthesis){
                stack.push(lparenthesis);
            }
            else if(isOperator(ch)){
               Object pop=stack.pop();
               char ch1=pop.toString().charAt(0);
               while(getPrecedence(ch1) >= getPrecedence(ch) ){
                   if(!stack.empty())stack.pop();
                   else break;
                   if(isOperator(ch1)){
                       output=output+ch1;
                   }
               }stack.push(ch);
            }
            else if(ch == rparenthesis){
                while(stack.pop().toString().charAt(0) != lparenthesis){
                    if(isOperator(stack.pop().toString().charAt(0)))
                    output=output+stack.pop();
                }                
            }
            else {
               System.out.print("error.");
            }
        }
        stack.clear();
        return output;
    }
}