字符串的四则运算表达式

    public static void main(String[] args) {        // 支持括号 小数 负数        String statement = "-10/(4.5+5.5)*(-4-6+20)/-2"; // 10/(-2) 也行        System.out.println(calculate(statement));    }    @SuppressWarnings("unchecked")    private static double calculate(String statement){        Object[] result = filter(statement);        // 运算数字        List<Double> numList = (List) result[0];        // 运算符        List<Character> symbolList = (List) result[1];        while (!symbolList.isEmpty()) {            int index = symbolList.indexOf('(');            if (index == -1) {                // 没有括号正常运算                realCalculate(numList, symbolList);            } else {                int right = symbolList.indexOf(')');                if (right == index + 1) {                    // 括号内的值都取完了，删除括号                    symbolList.remove(index);                    symbolList.remove(index);                    continue;                }                // 左右括号齐全 先算括号内的                if (right != -1) {                    List<Double> doubles = numList.subList(index, right);                    List<Character> subChars = symbolList.subList(index + 1, right);                    realCalculate(doubles, subChars);                }            }        }        return numList.get(0);    }    /**     * @return 一个包含数字的列表和一个包含运算符的列表     */    private static Object[] filter(String statement) {        // 形式 123,456,789 可能会有空字符串        StringBuilder nums = new StringBuilder();        // 符号列表        List<Character> symbolList = new LinkedList<>();        for (int i = 0; i < statement.length(); i++) {            char c = statement.charAt(i);            if (c == '-' && (i == 0 || statement.charAt(i - 1) == '('             || statement.charAt(i - 1) == '*' || statement.charAt(i - 1) == '/')) {                nums.append(c).append(statement.charAt(i + 1));                i++;            } else if (Character.isDigit(c) || c == '.') {                nums.append(c);            } else {                symbolList.add(c);                nums.append(',');            }        }        String[] ss = nums.toString().split(",");        List<Double> numList = new ArrayList<>();        for (String num : ss) {            if (!num.isEmpty()) {                numList.add(Double.parseDouble(num));            }        }        return new Object[]{numList, symbolList};    }    private static void realCalculate(List<Double> numList, List<Character> symbolList) {        while (!symbolList.isEmpty()) {            int index = symbolList.indexOf('*'), tmp;            double value = 0.0D;            if (index != -1 && (tmp = symbolList.indexOf('/')) != -1) {                // 同时出现 * / 从左至右运算                if (index < tmp) {                    value = numList.remove(index) * numList.remove(index);                } else {                    index = tmp;                    value = numList.remove(index) / numList.remove(index);                }            } else if (index != -1) {                value = numList.remove(index) * numList.remove(index);            } else if ((index = symbolList.indexOf('/')) != -1) {                value = numList.remove(index) / numList.remove(index);            } else if ((index = symbolList.indexOf('+')) != -1 && (tmp = symbolList.indexOf('-')) != -1) {                // 同时出现 + - 从左至右运算                if (index < tmp) {                    value = numList.remove(index) + numList.remove(index);                } else {                    index = tmp;                    value = numList.remove(index) - numList.remove(index);                }            } else if (index != -1) {                value = numList.remove(index) + numList.remove(index);            } else if ((index = symbolList.indexOf('-')) != -1) {                value = numList.remove(index) - numList.remove(index);            }            // 删除运算符            symbolList.remove(index);            // 将计算结果放回列表，待下次计算            numList.add(index, value);        }    }

总结一下

我的方法是先从括号的算起，根据运算符索引查找运算数索引，从而进行计算，算完后删除运算符和运算数，并将运算结果放回待运算的列表