两种格式化float的方式，不同的输出

float mAverageNumber = sum/12;
NumberFormat numFormat = NumberFormat.getNumberInstance();
numFormat.setMaximumFractionDigits(2);
String str = numFormat.format(mAverageNumber);
//above code output :$1,581.42
String str = String.valueOf((new BigDecimal(mAverageNumber)).setScale(2,BigDecimal.ROUND_HALF_UP));
//that output :$1581.42
System.out.println("$"+str);