import java.util.*;

public class PostfixEvaluation

{

  static boolean isOperator(char ch)

  {

      if(ch == '+' || ch == '-' || ch == '*' || ch == '/')

      return true;

      return false;

  }

  static void evaluatePostfix(String exp)

  {

      Stack<Integer> postFix = new Stack<>();    // Create postfix stack

      int n = exp.length();

      for(int i=0;i<n;i++)

      {

        if(isOperator(exp.charAt(i)))

        {

        // pop top 2 operands.

        int op1 = postFix.pop();

        int op2 = postFix.pop();

        // evaluate in reverse order i.e. op2 operator op1.

        switch(exp.charAt(i))

        {

            case '+': postFix.push(op2 + op1);

                      break;

            case '-': postFix.push(op2 - op1);

                      break;

            case '*': postFix.push(op2 * op1);

                      break;

            case '/': postFix.push(op2 / op1);

                      break;

        }

        }

        // Current Char is Operand simple push into stack

        else

        {

        // convert to integer

        int operand = exp.charAt(i) - '0';

        postFix.push(operand);

        }

      }

      // Stack at End will contain result.

      System.out.println(postFix.pop());

  }

  public static void main(String args[])

  {

      String exp = "823*+7/1-";

      System.out.print("The PostFix Evaluation for the Given Expression "+exp+" is: ");

      evaluatePostfix(exp);

  }

}

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