Java (Evaluate expression) Modify Listing 20.9 EvaluateExpression.java to add op

Question

Java

(Evaluate expression) Modify Listing 20.9 EvaluateExpression.java to add
operators ^ for exponent and % for modulus. For example, 3 ^ 2 is 9 and 3 % 2
is 1. The ^ operator has the highest precedence and the % operator has the same
precedence as the * and / operators. Your program should prompt the user to
enter an expression.

Here is a sample run of the program:
Enter an expression: (5 * 2 ^ 3 + 2 * 3 % 2) * 4
(5 * 2 ^ 3 + 2 * 3 % 2) * 4 = 160

Listing 20.9
import java.util.Stack;
import java.util.Scanner;

public class Beginning {
public static void main(String[] args) {
// Check number of arguments passed
      String[] go = {"(5+32)*4"};
if (go.length != 1) {
System.out.println(
"Usage: java EvaluateExpression "expression"");
System.exit(1);
}

try {
System.out.println(evaluateExpression(go[0]));
}
catch (Exception ex) {
System.out.println("Wrong expression: " + go[0]);
}
}

/** Evaluate an expression */
public static int evaluateExpression(String expression) {
// Create operandStack to store operands
Stack<Integer> operandStack = new Stack<>();

// Create operatorStack to store operators
Stack<Character> operatorStack = new Stack<>();

// Insert blanks around (, ), +, -, /, and *
expression = insertBlanks(expression);

// Extract operands and operators
String[] tokens = expression.split(" ");

// Phase 1: Scan tokens
for (String token: tokens) {
if (token.length() == 0) // Blank space
continue; // Back to the while loop to extract the next token
else if (token.charAt(0) == '+' || token.charAt(0) == '-') {
// Process all +, -, *, / in the top of the operator stack
while (!operatorStack.isEmpty() &&
(operatorStack.peek() == '+' ||
operatorStack.peek() == '-' ||
operatorStack.peek() == '*' ||
operatorStack.peek() == '/')) {
processAnOperator(operandStack, operatorStack);
}

// Push the + or - operator into the operator stack
operatorStack.push(token.charAt(0));
}
else if (token.charAt(0) == '*' || token.charAt(0) == '/') {
// Process all *, / in the top of the operator stack
while (!operatorStack.isEmpty() &&
(operatorStack.peek() == '*' ||
operatorStack.peek() == '/')) {
processAnOperator(operandStack, operatorStack);
}

   // Push the * or / operator into the operator stack
   operatorStack.push(token.charAt(0));
   }
   else if (token.trim().charAt(0) == '(') {
   operatorStack.push('('); // Push '(' to stack
   }
   else if (token.trim().charAt(0) == ')') {
   // Process all the operators in the stack until seeing '('
   while (operatorStack.peek() != '(') {
   processAnOperator(operandStack, operatorStack);
   }

   operatorStack.pop(); // Pop the '(' symbol from the stack
   }
   else { // An operand scanned
   // Push an operand to the stack
   operandStack.push(new Integer(token));
   }
   }

   // Phase 2: Process all the remaining operators in the stack
   while (!operatorStack.isEmpty()) {
   processAnOperator(operandStack, operatorStack);
   }

   // Return the result
   return operandStack.pop();
   }

   /** Process one operator: Take an operator from operatorStack and
   * apply it on the operands in the operandStack */
   public static void processAnOperator(
   Stack<Integer> operandStack, Stack<Character> operatorStack) {
   char op = operatorStack.pop();
   int op1 = operandStack.pop();
   int op2 = operandStack.pop();
   if (op == '+')
   operandStack.push(op2 + op1);
   else if (op == '-')
   operandStack.push(op2 - op1);
   else if (op == '*')
operandStack.push(op2 * op1);
else if (op == '/')
operandStack.push(op2 / op1);
}

public static String insertBlanks(String s) {
String result = "";

for (int i = 0; i < s.length(); i++) {
if (s.charAt(i) == '(' || s.charAt(i) == ')' ||
s.charAt(i) == '+' || s.charAt(i) == '-' ||
s.charAt(i) == '*' || s.charAt(i) == '/')
result += " " + s.charAt(i) + " ";
else
result += s.charAt(i);
}

return result;
}
}

Explanation / Answer

import java.util.Stack;
import java.util.Scanner;
import java.lang.Math;

public class Beginning {
   public static void main(String[] args) {
   // Check number of arguments passed
          String[] go = {"(5*2^3+2*3%2)*4"};
       if (go.length != 1) {
           System.out.println(
           "Usage: java EvaluateExpression "expression"");
           System.exit(1);
       }

       try {
           System.out.println(evaluateExpression(go[0]));
       }
       catch (Exception ex) {
           System.out.println("Wrong expression: " + go[0]);
       }
   }

/** Evaluate an expression */
   public static int evaluateExpression(String expression) {
   // Create operandStack to store operands
       Stack<Integer> operandStack = new Stack<>();

   // Create operatorStack to store operators
       Stack<Character> operatorStack = new Stack<>();

   // Insert blanks around (, ), +, -, /,^, %, and *
       expression = insertBlanks(expression);

   // Extract operands and operators
       String[] tokens = expression.split(" ");

// Phase 1: Scan tokens
   for (String token: tokens) {
       if (token.length() == 0) // Blank space
           continue; // Back to the while loop to extract the next token
       else if (token.charAt(0) == '+' || token.charAt(0) == '-') {
// Process all +, -, *, / in the top of the operator stack
           while (!operatorStack.isEmpty() &&
               (operatorStack.peek() == '+' ||
               operatorStack.peek() == '-' ||
               operatorStack.peek() == '*' ||
               operatorStack.peek() == '^' ||
               operatorStack.peek() == '%' ||
               operatorStack.peek() == '/')) {
               processAnOperator(operandStack, operatorStack);
           }

// Push the + or - operator into the operator stack
           operatorStack.push(token.charAt(0));
       }
       else if (token.charAt(0) == '*' || token.charAt(0) == '/' || token.charAt(0) == '%' ) {
       // Process all *, / in the top of the operator stack
           while (!operatorStack.isEmpty() &&
           (operatorStack.peek() == '*' ||
           operatorStack.peek() == '/' ||
           operatorStack.peek() == '%' ||
           operatorStack.peek() == '^' )) {
           processAnOperator(operandStack, operatorStack);
           }
      
   // Push the * or / operator into the operator stack
            operatorStack.push(token.charAt(0));
        }
       else if (token.charAt(0) == '^' ) {
       // Process all *, / in the top of the operator stack
           while (!operatorStack.isEmpty() &&
           (operatorStack.peek() == '^' )) {
           processAnOperator(operandStack, operatorStack);
           }
           operatorStack.push(token.charAt(0));
        }
      
           else if (token.trim().charAt(0) == '(') {
           operatorStack.push('('); // Push '(' to stack
           }
           else if (token.trim().charAt(0) == ')') {
           // Process all the operators in the stack until seeing '('
           while (operatorStack.peek() != '(') {
           processAnOperator(operandStack, operatorStack);
           }

           operatorStack.pop(); // Pop the '(' symbol from the stack
           }
   else { // An operand scanned
   // Push an operand to the stack
   operandStack.push(new Integer(token));
   }
   }

   // Phase 2: Process all the remaining operators in the stack
   while (!operatorStack.isEmpty()) {
   processAnOperator(operandStack, operatorStack);
   }

   // Return the result
   return operandStack.pop();
   }

   /** Process one operator: Take an operator from operatorStack and
   * apply it on the operands in the operandStack */
   public static void processAnOperator(
   Stack<Integer> operandStack, Stack<Character> operatorStack) {
   char op = operatorStack.pop();
   int op1 = operandStack.pop();
   int op2 = operandStack.pop();
   if (op == '+')
   operandStack.push(op2 + op1);
   else if (op == '-')
   operandStack.push(op2 - op1);
   else if (op == '*')
operandStack.push(op2 * op1);
else if (op == '/')
operandStack.push(op2 / op1);
else if (op == '^')
operandStack.push(pow(op2, op1));
else if (op == '%')
operandStack.push(op2 % op1);
}

   public static String insertBlanks(String s) {
       String result = "";

       for (int i = 0; i < s.length(); i++) {
           if (s.charAt(i) == '(' || s.charAt(i) == ')' || s.charAt(i) == '+' || s.charAt(i) == '-' || s.charAt(i) == '*' || s.charAt(i) == '/' || s.charAt(i) == '^' || s.charAt(i) == '%')
           result += " " + s.charAt(i) + " ";
           else
           result += s.charAt(i);
       }
  
       return result;
   }
}

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