java 计算数学公式

EvaluateMain.java

package com.junbaor.demo;

import java.util.Stack;

public class EvaluateMain {

    public static void main(String[] args) {
        //从左到右计算, 支持小括号
        System.out.println(calcEvaluate("(1+2+4)*3-(8+2)"));
    }

    public static int calcEvaluate(String evaluate) {
        evaluate = evaluate.replace(" ", "").trim();

        Stack<Integer> numericalStack = new Stack<>();
        Stack<Character> operationStack = new Stack<>();

        char[] chars = evaluate.toCharArray();
        for (char item : chars) {
            if (item == '+' || item == '-' || item == '*' || item == '/') {
                if (!operationStack.isEmpty() && operationStack.peek() != '(') {
                    calc(numericalStack, operationStack);
                }
                operationStack.push(item);
            } else if (item == '(') {
                operationStack.push(item);
            } else if (item == ')') {
                calc(numericalStack, operationStack);
                operationStack.pop();// 把左括号丢弃
            } else {
                numericalStack.push(Integer.valueOf(String.valueOf(item)));
            }
        }
        calc(numericalStack, operationStack);
        return numericalStack.pop();
    }

    public static void calc(Stack<Integer> numericalStack, Stack<Character> operationStack) {
        Integer pop2 = numericalStack.pop();
        Integer pop1 = numericalStack.pop();
        Character operation = operationStack.pop();

        if (operation == '+') {
            numericalStack.push(pop1 + pop2);
        } else if (operation == '-') {
            numericalStack.push(pop1 - pop2);
        } else if (operation == '*') {
            numericalStack.push(pop1 * pop2);
        } else if (operation == '/') {
            numericalStack.push(pop1 / pop2);
        }
    }
}