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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