please provide complete Java class code with main() function. Implement a progra

Question

please provide complete Java class code with main() function.

Implement a program that can input an expression in postfix notation (see ExerciseC-6.19) and output its value.

C-6.19 Postfix notation is an unambiguousway of writing an arithmetic expressionwithout

parentheses. It is defined so that if “(exp1)op(exp2)” is a normal fully parenthesized

expression whose operation is op, the postfix version of this is “pexp1

pexp2 op”, where pexp1 is the postfix version of exp1 and pexp2 is the postfix version

of exp2. The postfix version of a single number or variable is just that number

or variable. So, for example, the postfix version of “((5+2) (83))/4” is “5

2 + 8 3 4 /”. Describe a nonrecursive way of evaluating an expression in

postfix notation.

Explanation / Answer

For evaluation of postfix we use the stack class to push pop operations of the input numbers and the operators.

import java.util.*;
class EvalPostfx {
   private Stack inputStrngStck;
   private String inputStrng;
   private String otputStrng = "";
   public EvalPostfx(String in) {
      inputStrng = in;
      int stackSize = inputStrng.length(); //get the lenght of the string and assign tit to stack size
      inputStrngStck = new Stack(stackSize); //pull to the stack
   }
   public String evaluateStrng() {
      for (int j = 0; j < inputStrng.length(); j++) {
         char ch = inputStrng.charAt(j); //get each character of the input string
         switch (ch) {
            case '+':
            case '-':
               chckOprtr(ch, 1);
               break;
            case '*':
            case '/':
               chckOprtr(ch, 2);
               break;
            case '(':
               inputStrngStck.push(ch);
               break;
            case ')':
               gotParen(ch);
               break;
            default:
               otputStrng = otputStrng + ch;
               break;
         }
      }
      while (!inputStrngStck.isEmpty()) {
         otputStrng = otputStrng + inputStrngStck.pop();
      }
      //System.out.println(otputStrng);
      return otputStrng;
   }
   public void chckOprtr(char opThis, int prec1) {
      while (!inputStrngStck.isEmpty()) {
         char opTop = inputStrngStck.pop();
         if (opTop == '(') {
            inputStrngStck.push(opTop);
            break;
         } else {
            int prec2;
            if (opTop == '+' || opTop == '-')
            prec2 = 1;
            else
            prec2 = 2;
            if (prec2 < prec1) {
               inputStrngStck.push(opTop);
               break;
            }
            else otputStrng = otputStrng + opTop;
         }
      }
      inputStrngStck.push(opThis);
   }
   public void gotParen(char ch) {
      while (!inputStrngStck.isEmpty()) {
         char chx = inputStrngStck.pop();
         if (chx == '(')
         break;
         else otputStrng = otputStrng + chx;
      }
   }
   class Stack {
      private int maxSize;
      private char[] stackArray;
      private int top;
     
      public Stack(int max) {
         maxSize = max;
         stackArray = new char[maxSize];
         top = -1;
      }
      public void push(char j) {
         stackArray[++top] = j;
      }
      public char pop() {
         return stackArray[top--];
      }
      public boolean isEmpty() {
         return (top == -1);
      }
   }
   public static void main(String[] args) {
      String inputStrng ;
      String otputStrng;
      Scanner sc= new Scanner(System.in); //scanner class to read input
      System.out.println("Enter arthemetic expression to evaluate its postfix");
      inputStrng=sc.nextLine(); //read the input string
      EvalPostfx inStr = new EvalPostfx(inputStrng); //initialing object for evaluating the postfix
      otputStrng = inStr.evaluateStrng(); //calling the method to evaluate string
      System.out.println("The input expression is " + inputStrng + ' ');
      System.out.println("Postfix is " + otputStrng + ' ');
   }
}

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