public class MyCalculator {

 public static void main(String[] args) {
 String obj = "6+(8/2)+6/3+1*8 + 30";
 ArrayList<String> arrayList = strFormat(obj);
 System.out.println(obj + "=" + calculator(arrayList));
 }


 /**
 * 采用后續(xù)表達式計算結(jié)果
 * 1、當前字符串為數(shù)字時，直接入棧
 * 2、當前字符串為計算符時，取出棧中的前兩個計算
 * 3、將計算結(jié)果再放入到棧中，棧中最后剩余的一個元素就是要求的結(jié)果
 */
 private static int calculator(ArrayList<String> obj) {
 ArrayList<String> result = transform(obj);
 System.out.println(result);
 Stack<Integer> stack = new Stack<>();

 for (int i = 0; i < result.size(); i++) {
  String symbol = result.get(i);
  if (isDigital(symbol)) { //數(shù)字直接入棧
  stack.push(Integer.parseInt(symbol));
  } else { // 處理操作符
  int num1, num2;
  num1 = stack.pop(); //取出兩個數(shù)
  num2 = stack.pop();
  switch (symbol) {
   case "+":
   stack.push(num2 + num1);
   break;
   case "-":
   stack.push(num2 - num1);
   break;
   case "*":
   stack.push(num2 * num1);
   break;
   case "/":
   stack.push(num2 / num1);
   break;
   default:
   break;
  }
  }
 }
 return stack.pop();
 }

 /**
 * 中序遍歷改為后續(xù)遍歷
 */
 private static ArrayList<String> transform(ArrayList<String> arrayList) {
 Stack<String> stack = new Stack<>();
 ArrayList<String> result = new ArrayList<>();
 for (int index = 0; index < arrayList.size(); index++) {
  String symbol = arrayList.get(index);
  if (isDigital(symbol)) { //如果是數(shù)字直接輸出
  result.add(symbol);
  } else if (symbol.equals(")")) {
  String tmp;
  while (!(tmp = stack.pop()).equals("(")) { // 匹配成功后停止
   result.add(tmp);
  }
  } else {
  if (stack.isEmpty()) {
   stack.push(symbol);
   continue;
  }
  String tmp = stack.peek();
  while (outPriority(symbol) <= inPriority(tmp)) { //優(yōu)先級小于棧內(nèi)優(yōu)先級，一直出棧
   result.add(tmp);
   stack.pop();
   if (stack.isEmpty()) {
   break;
   }
   tmp = stack.peek();
  }
  stack.push(symbol);
  }
 }
 //將剩余的出棧
 while (!stack.isEmpty()) {
  result.add(stack.pop());
 }
 return result;
 }

 /**
 * 首先對String 進行格式化 轉(zhuǎn)化成ArrayList
 * @param src 3*5+8;
 * @return ArrayList 3 * 5 + 8
 */
 private static ArrayList<String> strFormat(String src) {
 if (src == null || src.equals("")) {
  return null;
 }
 ArrayList<String> arrayList = new ArrayList<>();
 StringBuilder comChar = new StringBuilder();
 for (int i = 0; i <src.length(); i++) {
  char ch = src.charAt(i);
  if (ch == ' ') {
  continue; //去除空格
  }
  if (!Character.isDigit(ch)) {
  if (!comChar.toString().trim().equals("")) {
   arrayList.add(comChar.toString().trim());
   comChar.delete(0, comChar.length());
  }
  arrayList.add(ch + "");
  continue;
  }
  comChar.append(ch);
 }
 if (!comChar.toString().trim().equals("")) {
  arrayList.add(comChar.toString().trim());
 }
 return arrayList;
 }

 /**
 * 判斷是否為數(shù)字
 * @param symbol 782 或者 + - * /
 * @return true or false
 */
 private static boolean isDigital(String symbol) {
 return !symbol.equals("+") && !symbol.equals("-")
  && !symbol.equals("*") && !symbol.equals("/")
  && !symbol.equals("(") && !symbol.equals(")");
 }

 private static int inPriority(String ch) {
 switch (ch) {
  case "+":
  case "-":
  return 2;
  case "*":
  case "/":
  return 4;
  case ")":
  return 7;
  case "(":
  return 1;
  default:
  return 0;
 }
 }

 private static int outPriority(String ch) {
 switch (ch) {
  case "+":
  case "-":
  return 3;
  case "*":
  case "/":
  return 5;
  case ")":
  return 1;
  case "(":
  return 7;
  default:
  return 0;
 }
 }
}