Java实现计算器的代码

用java 实现的计算器，原理看代码注释，具体内容如下

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));
 }


 /**
  * 采用后续表达式计算结果
  * 1、当前字符串为数字时，直接入栈
  * 2、当前字符串为计算符时，取出栈中的前两个计算
  * 3、将计算结果再放入到栈中，栈中最后剩余的一个元素就是要求的结果
  */
 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)) { //数字直接入栈
    stack.push(integer.parseint(symbol));
   } else { // 处理操作符
    int num1, num2;
    num1 = stack.pop(); //取出两个数
    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();
 }

 /**
  * 中序遍历改为后续遍历
  */
 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)) { //如果是数字直接输出
    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)) { //优先级小于栈内优先级，一直出栈
     result.add(tmp);
     stack.pop();
     if (stack.isempty()) {
      break;
     }
     tmp = stack.peek();
    }
    stack.push(symbol);
   }
  }
  //将剩余的出栈
  while (!stack.isempty()) {
   result.add(stack.pop());
  }
  return result;
 }

 /**
  * 首先对string 进行格式化 转化成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;
 }

 /**
  * 判断是否为数字
  * @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;
  }
 }
}

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