Java版的Eval

import java.util.ArrayList;import java.util.Stack;public class Eval {private final static String ERR_NOT_END_VALID = "The last character of your expression MUST be '#'!";private final static String ERR_PARENTHESE_NOT_PAIR = "'(' & ')' should be used in pair!";private final static String ERR_CHAR_NOT_SUPPORT = "Not supported character";private final static String ERR_OPERATION_NOT_SUPPORTED = "Not supported operation";private final static String ERR_OPERATOR_NOT_VALID = " doesn't support double data!";private final static String ERR_UNKNOWN = "An unknown error!";private static boolean flag_double;/* * expression must be end with # */public static String eval(String expression) {ArrayList<String> list;try {list = toSuffixSequence(expression);return calculate(list);} catch (Exception e) {e.printStackTrace();return null;}}public static boolean isResultDouble(){return flag_double;}private static String calculate(ArrayList<String> list) throws Exception {Stack<String> stack = new Stack<String>();for (String s : list) {if (isOperator(s)) {String d1 = stack.pop();String d2 = stack.pop();String res = doCalc(d2, d1, s);stack.push(res);} elsestack.push(s);}if (stack.size() == 1)return stack.pop();elsethrow new Exception(ERR_UNKNOWN);}private static String doCalc(String d1, String d2, String oper) throws Exception {if (oper != null && oper.length() > 1)throw new Exception(ERR_OPERATION_NOT_SUPPORTED + ":'" + oper + "'");flag_double = isDoubleNeeded(d1, d2, oper);switch (oper.charAt(0)) {case '+':if (flag_double)return Double.toString(Double.parseDouble(d1)+ Double.parseDouble(d2));elsereturn Integer.toString(Integer.parseInt(d1)+ Integer.parseInt(d2));case '-':if (flag_double)return Double.toString(Double.parseDouble(d1)- Double.parseDouble(d2));elsereturn Integer.toString(Integer.parseInt(d1)- Integer.parseInt(d2));case '*':if (flag_double)return Double.toString(Double.parseDouble(d1)* Double.parseDouble(d2));elsereturn Integer.toString(Integer.parseInt(d1)* Integer.parseInt(d2));case '/':if (flag_double)return Double.toString(Double.parseDouble(d1)/ Double.parseDouble(d2));elsereturn Integer.toString(Integer.parseInt(d1)/ Integer.parseInt(d2));case '%':if (flag_double)throw new Exception("'%' " + ERR_OPERATOR_NOT_VALID);elsereturn Integer.toString(Integer.parseInt(d1)+ Integer.parseInt(d2));default:throw new Exception(ERR_OPERATION_NOT_SUPPORTED + ":'" + oper + "'");}}private static boolean isDoubleNeeded(String d1, String d2, String oper) {if (d1.contains(".") || d2.contains("."))return true;if (oper != null && oper.equals("/")) {int left = Integer.parseInt(d1) % Integer.parseInt(d2);if (left != 0)return true;}return false;}private static boolean isOperator(String str) {if (str != null&& (str.equals("+") || str.equals("-") || str.equals("*")|| str.equals("/") || str.equals("%")))return true;return false;}private static ArrayList<String> toSuffixSequence(String expression)throws Exception {if (!expression.endsWith("#"))throw new Exception(ERR_NOT_END_VALID);ArrayList<String> list = new ArrayList<String>();Stack<String> stack = new Stack<String>();stack.push("#");char last, ch;StringBuffer sb = null;for (int i = 0; i < expression.length(); i++) {ch = expression.charAt(i);switch (ch) {case '+':case '-':case '*':case '/':case '%':last = stack.peek().charAt(0);if (last != '(' && priority(last) >= priority(ch))list.add(stack.pop());stack.push("" + ch);break;case '(':stack.push("(");break;case ')':while (!stack.isEmpty() && stack.peek().charAt(0) != '(')list.add(stack.pop());if (stack.isEmpty() || stack.size() == 1)throw new Exception(ERR_PARENTHESE_NOT_PAIR);stack.pop();break;case '#':while (stack.size() > 1 && stack.peek().charAt(0) != '(')list.add(stack.pop());if (stack.size() > 1)throw new Exception(ERR_PARENTHESE_NOT_PAIR);break;default:if (Character.isDigit(ch) || '.' == ch) {sb = new StringBuffer();sb.append(ch);while (Character.isDigit(expression.charAt(i+1)) || expression.charAt(i+1) == '.')sb.append(expression.charAt(++i));list.add(sb.toString());break;} elsethrow new Exception(ERR_CHAR_NOT_SUPPORT + ":'" + ch + "'");}}return list;}private static int priority(char ch) {switch (ch) {case '+':case '-':return 1;case '*':case '/':case '%':return 2;case '#':return 0;default:return 0;}}public static void main(String[] args) {String expression = "2*2+7*2-10*2#";try {System.out.println(Eval.eval(expression));} catch (Exception e) {e.printStackTrace();}}}