Java中通過BigDecimal實現float浮點型保留2位小數或者其它指定位數

float f = 2.546546546454564f;
BigDecimal b = new BigDecimal(influCount);  
f = b.setScale(2, BigDecimal.ROUND_HALF_UP).floatValue(); 
System.out.println(f);

輸出結果爲2.55。

BigDecmal類setScale()方法說明參考下圖：

參數定義

ROUND_CEILING 
Rounding mode to round towards positive infinity. 
向正無窮方向舍入 

ROUND_DOWN 
Rounding mode to round towards zero. 
向零方向舍入 

ROUND_FLOOR 
Rounding mode to round towards negative infinity. 
向負無窮方向舍入 

ROUND_HALF_DOWN 
Rounding mode to round towards "nearest neighbor" unless both neighbors are equidistant, in which case round down. 
向（距離）最近的一邊舍入，除非兩邊（的距離）是相等,如果是這樣，向下舍入, 例如1.55 保留一位小數結果爲1.5 

ROUND_HALF_EVEN 
Rounding mode to round towards the "nearest neighbor" unless both neighbors are equidistant, in which case, round towards the even neighbor. 
向（距離）最近的一邊舍入，除非兩邊（的距離）是相等,如果是這樣，如果保留位數是奇數，使用ROUND_HALF_UP ，如果是偶數，使用ROUND_HALF_DOWN 


ROUND_HALF_UP 
Rounding mode to round towards "nearest neighbor" unless both neighbors are equidistant, in which case round up. 
向（距離）最近的一邊舍入，除非兩邊（的距離）是相等,如果是這樣，向上舍入, 1.55保留一位小數結果爲1.6 


ROUND_UNNECESSARY 
Rounding mode to assert that the requested operation has an exact result, hence no rounding is necessary. 
計算結果是精確的，不需要舍入模式 


ROUND_UP 
Rounding mode to round away from zero. 
向遠離0的方向舍入