保留小数点位数和格式
JS 中

1. double运算
c = parseFloat(a) + parseFloat(b))

2. 四舍五入，保留两位小数
c = c.toFixed(2);

3. 去掉小数点后面多余的0
c = c.toFixed(2)*100/100;


JAVA中

//四舍五入，保留指定小数位public static Double roundDouble(Object obj, int scale){double d = 0; try{d  = Double.parseDouble(obj.toString().replaceAll(",", ""));  } catch (Exception e) {  d = 0;  }//四舍五入，保留两位小数BigDecimal bd = new BigDecimal(d);  bd = bd.setScale(scale, BigDecimal.ROUND_HALF_UP);d = bd.doubleValue();   return d;}//转成字符串，去掉科学计数法public static String roundFormat(Object obj){ String str = "0"; try{Double d  = Double.parseDouble(obj.toString().replaceAll(",", "")); //四舍五入，保留两位小数BigDecimal bd = new BigDecimal(d);  bd = bd.setScale(2, BigDecimal.ROUND_HALF_UP);d = bd.doubleValue();       //去除科学计数法 DecimalFormat df = new DecimalFormat("#.##"); str = df.format(d);  } catch (Exception e) {  str = "0";  }    return str; }//除法public static Double divideRound(Double a, Double b){try {if (b == 0) {return 0.0;} else {BigDecimal bd = new BigDecimal(a/b);          bd = bd.setScale(2, BigDecimal.ROUND_HALF_UP);          double d = bd.doubleValue();          bd = null;          return d;  }} catch (Exception e) {  return 0.0;  }}