LISTING 20.12:

import java.util.Stack;

public static void main(String[] args) { //Check number of arguments passed if (args.length != 1) { System.out.println("Usage: java EvaluateExpression "expression""); System.exit(1); } try { System.out.println(evaluateExpression(args[0])); } catch (Exception ex) { System.out.println("Wrong expression: " + args[0]); } } /** Evaluate an expression */ public static int evaluateExpression(String expression) { //Create operandStack to store operands Stack operandStack = new Stack(); //Create operandStack to store operators Stack 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 the operatorStack and * apply it on the operands in the operandStack */ public static void processAnOperator(Stack operandStack, Stack 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

Modify Listing 20.12 EvaluateExpression-Java to add operators ^ for exponent and 96 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. Have the program display the output to the console. Your output should be as shown in the below example. Text in green is input by the user at run time. Text in black is output produced by the program. Enter the expression to be evaluated : (5*2^342*3%2)#4 (5*2^3+2*3%2)*4 160