Answer and Explanation:
/**POSTFIX CALCULATION IN JAVA ****/
import java.io.*;
import java.util.*;
import java.lang.*;
public class ReversePolishIMP
{
//main
public static void main(String[] args)
{
//DECLARE VARIABLE
int opnd1;
int opnd2;
int rst=0;
//SCANNER TO READ POSTFIX STRING
Scanner revScan=new Scanner(System.in);
String postFix;
//ASK REPEATEDLY
while(true)
{
System.out.println("Enter a reverse polish expressio nor quit to quit");
postFix=revScan.nextLine();
//CHAECK FOR PROGRAM quit
if(postFix.equals("quit"))
{
System.out.println("Goodbye");
break;
}
//CREATE STACK TO STORE OPERANDS
Stack<String> stringStack=new Stack<String>();
//SPLIT THE STRING
String[] t = postFix.split(" ");
//PROCESS POSTFIX
for(int k = 0; k < t.length; k++)
{
String tok = t[k];
//FIND OPERAND
if (!"+".equals(tok) && !"*".equals(tok) && !"-".equals(tok) && !"/".equals(tok))
stringStack.push(tok);
else
{
//PERFORM ADDITION, SUBTRACTION,MULTIPLICCATION,DIVISION
String calOptr = t[k];
opnd1 = Integer.parseInt(stringStack.pop());
opnd2 = Integer.parseInt(stringStack.pop());
if (calOptr.equals("/"))
rst = opnd1 / opnd2;
else if(calOptr.equals("*"))
rst = opnd1 * opnd2;
else if(calOptr.equals("+"))
rst = opnd1 + opnd2;
else if(calOptr.equals("-"))
rst = opnd2 - opnd1;
else System.out.println("Illeagal symbol");
//STORE RESULT IN STACK
stringStack.push(Integer.toString(rst));
}
}
//GET FINAL RESULT
rst=Integer.parseInt(stringStack.pop());
//CHECK FOR EMPTY STACK
if(!stringStack.isEmpty())
{
System.out.println("THIS WAS NOT PROPERLY FORMATTED");
System.out.println("0");
}
else
System.out.println(rst);
}
}
}
