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 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 obj) {

arraylist result = transform(obj);

system.out.println(result);

stack 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 transform(arraylist arraylist) {

stack stack = new stack<>();

arraylist 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 strformat(string src) {

if (src == null || src.equals("")) {

return null;

}

arraylist arraylist = new arraylist<>();

stringbuilder comchar = new stringbuilder();

for (int i = 0; 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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