public static void main(String[] args) {
//      BigDecimal四舍五入
        BigDecimal a = new BigDecimal("3.34543");
        BigDecimal bigDecimal = a.setScale(2, BigDecimal.ROUND_HALF_UP);
        System.out.println(bigDecimal);
        //向下取整,保留2位小数
        String num = "2.345";
        double floor = Math.floor(Double.valueOf(num));
        String format = String.format("%.2f", floor);
        System.out.println(format);
    }

    public BigDecimal bigDecimalToRound(BigDecimal bigDecimal, int newScale) {
        return bigDecimal.setScale(newScale, BigDecimal.ROUND_HALF_UP);
    }

    public String stringToFloor(String str) {
        return String.format("%.2f", Math.floor(Double.valueOf(str)));
    }