Map<String, Map<String, String>>

/**
 * 查表得到op1和op2的優(yōu)先級(jí)
 * @param op1 運(yùn)算符1
 * @param op2 運(yùn)算符2
 * @return ">", "<" 或 "="
 */
public String priority(String op1, String op2) {
 return priorityMap.get(op1).get(op2);
}

/**
 * 算術(shù)表達(dá)式求值。
 * 3 + 4 * 12 結(jié)果為51
 * @author whf
 *
 */
public class EvaluateExpression {
 // 運(yùn)算符優(yōu)先級(jí)關(guān)系表
 private Map<String, Map<String, String>> priorityMap = new HashMap<String, Map<String, String>>();
 private LinkedStack<String> optStack = new LinkedStack<String>();
 // 運(yùn)算符棧
 private LinkedStack<Double> numStack = new LinkedStack<Double>();
 // 操作數(shù)棧
 /**
  * 計(jì)算表達(dá)式
  * @param exp 四則運(yùn)算表達(dá)式, 每個(gè)符號(hào)必須以空格分隔
  * @return
  */
 public double calcualte(String exp) {
  StringTokenizer st = new StringTokenizer(exp);
  while (st.hasMoreTokens()) {
   String token = st.nextToken();
   process(token);
  }
  return numStack.pop();
 }
 /**
  * 讀入一個(gè)符號(hào)串。
  * 如果是數(shù)字，則壓入numStack
  * 如果是運(yùn)算符，則將optStack棧頂元素與該運(yùn)算符進(jìn)行優(yōu)先級(jí)比較
  * 如果棧頂元素優(yōu)先級(jí)低，則將運(yùn)算符壓入optStack棧,如果相同，則彈出左括號(hào)，如果高，則取出２個(gè)數(shù)字，取出一個(gè)運(yùn)算符執(zhí)行計(jì)算，然后將結(jié)果壓入numStack棧中
  * @param token
  */
 private void process(String token) {
  while (false == "#".equals(optStack.getTop()) || false == token.equals("#")) {
   // token is numeric
   if (true == isNumber(token)) {
        numStack.push(Double.parseDouble(token));
        break;
        // token is operator
   } else {
        String priority = priority(optStack.getTop(), token);
        if ("<".equals(priority)) {
         optStack.push(token);
         break;
        } else if ("=".equals(priority)) {
         optStack.pop();
         break;
        } else {
          double res = calculate(optStack.pop(), numStack.pop(), numStack.pop());
          numStack.push(res);
        }
   }
  }
 }
 /**
  * 執(zhí)行四則運(yùn)算
  * @param opt
  * @param n1
  * @param n2
  * @return
  */
 private double calculate(String opt, double n1, double n2) {
  if ("+".equals(opt)) {
   return n2 + n1;
  } else if ("-".equals(opt)) {
   return n2 - n1;
  } else if ("*".equals(opt)) {
   return n2 * n1;
  } else if ("/".equals(opt)) {
   return n2 / n1;
  } else {
   throw new RuntimeException("unsupported operator:" + opt);
  }
 }
 /**
  * 檢查一個(gè)String是否為數(shù)字
  * @param token
  * @return
  */
 private boolean isNumber(String token) {
  int LEN = token.length();
  for (int ix = 0 ; ix < LEN ; ++ix) {
   char ch = token.charAt(ix);
   // 跳過(guò)小數(shù)點(diǎn)
   if (ch == '.') {
    continue;
   }
   if (false == isNumber(ch)) {
    return false;
   }
  }
  return true;
 }
 /**
  * 檢查一個(gè)字符是否為數(shù)字
  * @param ch
  * @return
  */
 private boolean isNumber(char ch) {
  if (ch >= '0' && ch <= '9') {
   return true;
  }
  return false;
 }
 /**
  * 查表得到op1和op2的優(yōu)先級(jí)
  * @param op1 運(yùn)算符1
  * @param op2 運(yùn)算符2
  * @return ">", "<" 或 "="
  */
 public String priority(String op1, String op2) {
  return priorityMap.get(op1).get(op2);
 }
 /**
  * 構(gòu)造方法，初始化優(yōu)先級(jí)表
  */
 public EvaluateExpression() {
  // initialize stack
  optStack.push("#");
  // initialize priority table
  // +
  Map<String, String> subMap = new HashMap<String, String>();
  subMap.put("+", ">");
  subMap.put("-", ">");
  subMap.put("*", "<");
  subMap.put("/", "<");
  subMap.put("(", "<");
  subMap.put(")", ">");
  subMap.put("#", ">");
  priorityMap.put("+", subMap);
  // -
  subMap = new HashMap<String, String>();
  subMap.put("+", ">");
  subMap.put("-", ">");
  subMap.put("*", "<");
  subMap.put("/", "<");
  subMap.put("(", "<");
  subMap.put(")", ">");
  subMap.put("#", ">");
  priorityMap.put("-", subMap);
  // *
  subMap = new HashMap<String, String>();
  subMap.put("+", ">");
  subMap.put("-", ">");
  subMap.put("*", ">");
  subMap.put("/", ">");
  subMap.put("(", "<");
  subMap.put(")", ">");
  subMap.put("#", ">");
  priorityMap.put("*", subMap);
  // /
  subMap = new HashMap<String, String>();
  subMap.put("+", ">");
  subMap.put("-", ">");
  subMap.put("*", ">");
  subMap.put("/", ">");
  subMap.put("(", "<");
  subMap.put(")", ">");
  subMap.put("#", ">");
  priorityMap.put("/", subMap);
  // (
  subMap = new HashMap<String, String>();
  subMap.put("+", "<");
  subMap.put("-", "<");
  subMap.put("*", "<");
  subMap.put("/", "<");
  subMap.put("(", "<");
  subMap.put(")", "=");
  //subMap.put("#", ">");
  priorityMap.put("(", subMap);
  // )
  subMap = new HashMap<String, String>();
  subMap.put("+", ">");
  subMap.put("-", ">");
  subMap.put("*", ">");
  subMap.put("/", ">");
  //subMap.put("(", "<");
  subMap.put(")", ">");
  subMap.put("#", ">");
  priorityMap.put(")", subMap);
  // #
  subMap = new HashMap<String, String>();
  subMap.put("+", "<");
  subMap.put("-", "<");
  subMap.put("*", "<");
  subMap.put("/", "<");
  subMap.put("(", "<");
  //subMap.put(")", ">");
  subMap.put("#", "=");
  priorityMap.put("#", subMap);
 }
}

String exp = "4 * ( 10 + 2 ) + 1 #";
EvaluateExpression ee = new EvaluateExpression();
out.println(ee.calcualte(exp));