I can't Figure out why my program not working. When I run it shows Usage: java EvaluateExpression "expression"

import java.util.Stack;

public class EvaluateExpression { 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 operatorStack 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() == '/'|| 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) =='^') { 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.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 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); else if(op=='%') operandStack.push(op2%op1); else if(op=='^'){ operandStack.push((int)Math.pow((double)op2,(double)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; } }