【java】多项式计算（中缀转后缀）

Calculator.java：

package calculator;

import java.util.Stack;

public class Calculator {
    /**
     * 转为后缀
     * @param exper 中缀表达式
     * @return
     * @throws Exception
     */
    public String postfixExpression(String exper) throws Exception {
        String exper_h = "";
        Stack<Character> symbol = new Stack<>();
        for (int i = 0; i < exper.length(); i++) {
            if (exper.charAt(i) >= '0' && exper.charAt(i) <= '9' || exper.charAt(i) == '.') {// 数字
                exper_h += exper.charAt(i);
            } else {// 符号
                exper_h += " ";
                if (exper.charAt(i) == '(') {
                    symbol.push(exper.charAt(i));
                    continue;
                }
                if (exper.charAt(i) == ')') {
                    while (!symbol.empty() && symbol.peek() != '(')
                        exper_h += symbol.pop();
                } else
                    while (!symbol.empty() && priority(symbol.peek()) >= priority(exper.charAt(i))) {
                        exper_h += symbol.pop();
                    }
                symbol.push(exper.charAt(i));
            }
        }
        while (!symbol.empty()) {
            exper_h += symbol.pop();
        }
        exper_h = exper_h.replace("(", "").replace(")", "").replaceAll(" +", " ");
        return exper_h;
    }
    /**
     * 计算结果
     * @param exper_h 后缀表达式
     * @return
     * @throws Exception
     */
    public Float calculation(String exper_h) throws Exception {
        Stack<String> number = new Stack<>();
        String temp = "";
        for (int i = 0; i < exper_h.length(); i++) {

            if (exper_h.charAt(i) >= '0' && exper_h.charAt(i) <= '9' || exper_h.charAt(i) == '.'
                    || exper_h.charAt(i) == ' ') {
                temp += exper_h.charAt(i);
                if (exper_h.charAt(i + 1) == ' ') {
                    number.push(temp);
                    temp = "";
                    i++;
                } else if (isSymbol(exper_h.charAt(i + 1))) {
                    number.push(temp);
                    temp = "";
                }
            } else {
                float val1 = Float.valueOf(number.pop());
                float val2 = Float.valueOf(number.pop());
                number.push(col(val2, val1, exper_h.charAt(i)).toString());
            }
        }
        return Float.valueOf(number.pop());
    }
    /**
     * 优先级
     * 
     * @param c
     * @return
     * @throws Exception
     */
    public int priority(char c) throws Exception {
        if (c == '(' || c == ')')
            return -1;
        if (c == '*' || c == '/')
            return 2;
        else if (c == '+' || c == '-')
            return 1;
        else if (c == ' ') {
            return 0;
        } else
            throw new Exception();
    }
    /**
     * 计算
     * @param val1
     * @param val2
     * @param c
     * @return
     * @throws Exception
     */
    public Float col(Float val1, Float val2, char c) throws Exception {
        if (c == '*') {
            return val1 * val2;
        } else if (c == '/') {
            return val1 / val2;
        } else if (c == '+') {
            return val1 + val2;
        } else if (c == '-') {
            return val1 - val2;
        } else
            throw new Exception();

    }
    /**
     * 符号检查
     * @param c
     * @return
     */
    public boolean isSymbol(char c) {
        return c == '+' || c == '-' || c == '*' || c == '/' || c == '(' || c == ')';
    }
}

Main:

package calculator;

import java.util.Stack;

public class Main {

    public static void main(String[] args) throws Exception {
        String exper = "1+1-(1*2+3-4/2)-1";
        Calculator ca =new Calculator();
        String exper_h = ca.postfixExpression(exper);
        System.out.println(ca.calculation(exper_h))```
//输出：0.0
    }
}