java常用工具方法

double类型后补0

private String roundByScale(double v, int scale) {
    if (scale < 0) {
        throw new IllegalArgumentException(
                "The   scale   must   be   a   positive   integer   or   zero");
    }
    if(scale == 0){
        return new DecimalFormat("0").format(v);
    }
    String formatStr = "0.";
    for(int i = 0; i < scale; i++){
        formatStr = formatStr + "0";
    }
    return new DecimalFormat(formatStr).format(v);
}