yuhaibo736

package com.cbd.dk.test;

import java.util.ListIterator;
import java.util.Stack;

public class Test {

 private String src;

 public Test(String src) {
  this.src = src;
 }
 public double getResult() {
  String postfix = getPostfix();
  Stack<String> stk = new Stack<String>();
  //System.out.println(postfix);
  String parts[] = postfix.split(" +");
  double result=0;
  for(int i=0; i<parts.length; i++){
   char tmp = parts[i].charAt(0);
   if(!isOperator(tmp)){
    stk.push(parts[i]);
   }else{
    double a = Double.parseDouble(stk.pop());
    double b = Double.parseDouble(stk.pop());
    result = calculate(b,a,tmp);
    stk.push(String.valueOf(result));
   }
  }
  return result;
 }

 /**
  * test if the character is an operator,such +,-,*,/
  * @param op  the character to test
  * @return  true if op is an operator otherwise false
  */
 private boolean isOperator(char op){
  return (op=='+'||op=='-'||op=='*'||op=='/');
 }

 /**
  * calculate an expression such (a op b)
  * @param a  number 1
  * @param b  number 2
  * @param op the operator
  * @return  (double)(a op b)
  */
 public double calculate(double a, double b, char op) {
  switch (op) {
   case '+':
    return a + b;
   case '-':
    return a - b;
   case '*':
    return a * b;
   case '/':
    return a / b;
  }
  return -1;
 }

 /**
  * convert the suffix to postfix
  * @return the postfix as a string
  */
 private String getPostfix() {
  Stack<String> stk = new Stack<String>();
  String postfix = new String();
  char op;
  int i = 0;
  while (i < src.length()) {
   if (Character.isDigit(src.charAt(i))||src.charAt(i)=='.') {
    postfix += " ";
    do {
     postfix += src.charAt(i++);
    } while ((i < src.length()) && (Character.isDigit(src.charAt(i))));
    postfix += " ";
   }else {
    switch (op = src.charAt(i++)) {
     case '(':
      stk.push("(");
      break;
     case ')':
      while (stk.peek() != "(") {
       String tmp = stk.pop();
       postfix += tmp;
       if(tmp.length()==1 && isOperator(tmp.charAt(0)))
        postfix += " ";
      }
      stk.pop();
      postfix += " ";
      break;
     case '+':
     case '-':
      while ((!stk.empty()) && (stk.peek() != "(")) {
       postfix += stk.pop()+" ";
      }
      stk.push(new Character(op).toString());
      break;
     case '*':
     case '/':
      while ((!stk.empty()) && ((stk.peek() == "*") || (stk.peek() == "/"))) {
       postfix += stk.pop()+" ";
      }
      stk.push(new Character(op).toString());
      break;
    }
   }
  }
  ListIterator it = stk.listIterator(stk.size());
  while (it.hasPrevious())
   postfix += it.previous() + " ";
  return postfix.trim().replaceAll(" +\\.",".");
 }

 /**
  * main function
  * @param args
  */
 public static void main(String args[]) {
  //System.out.println(new Test("((1.5+6.000)*9+9.36)*(8-8*8+8*7)").getResult());
  System.out.println(new Test("(2+(3*2)/2)").getResult());
 }
}