用java 实现的计算器，原理看代码注释，具体内容如下
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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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原文链接：https://blog.csdn.net/owenchan1987/article/details/79077333
