1. BigDecimal num1 = new BigDecimal(2.225667);//這種寫法不允許，會造成精度損失
2. BigDecimal num2 = new BigDecimal(2);//這種寫法是可以的
3. BigDecimal num = new BigDecimal("2.225667");//一般都會這樣寫最好
4. int count = num.scale();
System.out.println(count);//6 返回的是小數點后位數
好了，下面開始正式介紹知識點啦~~~~~~
1. ROUND_DOWN
-
BigDecimal b =
new BigDecimal(
"2.225667").setScale(
2, BigDecimal.ROUND_DOWN);
-
System.out.println(b);
//2.22 直接去掉多余的位數
2. ROUND_UP
-
BigDecimal c =
new BigDecimal(
"2.224667").setScale(
2, BigDecimal.ROUND_UP);
-
System.out.println(c);
//2.23 跟上面相反，進位處理
3. ROUND_CEILING
天花板（向上），正數進位向上，負數舍位向上
-
BigDecimal f =
new BigDecimal(
"2.224667").setScale(
2, BigDecimal.ROUND_CEILING);
-
System.out.println(f);
//2.23 如果是正數，相當於BigDecimal.ROUND_UP
-
-
BigDecimal g =
new BigDecimal(
"-2.225667").setScale(
2, BigDecimal.ROUND_CEILING);
-
System.out.println(g);
//-2.22 如果是負數，相當於BigDecimal.ROUND_DOWN
4. ROUND_FLOOR
地板（向下），正數舍位向下，負數進位向下
-
BigDecimal h =
new BigDecimal(
"2.225667").setScale(
2, BigDecimal.ROUND_FLOOR);
-
System.out.println(h);
//2.22 如果是正數，相當於BigDecimal.ROUND_DOWN
-
-
BigDecimal i =
new BigDecimal(
"-2.224667").setScale(
2, BigDecimal.ROUND_FLOOR);
-
System.out.println(i);
//-2.23 如果是負數，相當於BigDecimal.ROUND_HALF_UP
5. ROUND_HALF_UP
-
BigDecimal d =
new BigDecimal(
"2.225").setScale(
2, BigDecimal.ROUND_HALF_UP);
-
System.out.println(
"ROUND_HALF_UP"+d);
//2.23 四舍五入（若舍棄部分>=.5，就進位）
6. ROUND_HALF_DOWN
-
BigDecimal e =
new BigDecimal(
"2.225").setScale(
2, BigDecimal.ROUND_HALF_DOWN);
-
System.out.println(
"ROUND_HALF_DOWN"+e);
//2.22 四舍五入（若舍棄部分>.5,就進位）
7. ROUND_HALF_EVEN
-
BigDecimal j =
new BigDecimal(
"2.225").setScale(
2, BigDecimal.ROUND_HALF_EVEN);
-
System.out.println(j);
//2.22 如果舍棄部分左邊的數字為偶數，則作 ROUND_HALF_DOWN
-
-
BigDecimal k =
new BigDecimal(
"2.215").setScale(
2, BigDecimal.ROUND_HALF_EVEN);
-
System.out.println(k);
//2.22 如果舍棄部分左邊的數字為奇數，則作 ROUND_HALF_UP
-
-
-
System.out.println(
"************************************");
-
-
System.out.println(
"4.05: "+
new BigDecimal(
"4.05").setScale(
1, BigDecimal.ROUND_HALF_EVEN));
//4.05: 4.0 down
-
System.out.println(
"4.15: "+
new BigDecimal(
"4.15").setScale(
1, BigDecimal.ROUND_HALF_EVEN));
//4.15: 4.2 up
-
System.out.println(
"4.25: "+
new BigDecimal(
"4.25").setScale(
1, BigDecimal.ROUND_HALF_EVEN));
//4.25: 4.2 down
-
System.out.println(
"4.35: "+
new BigDecimal(
"4.35").setScale(
1, BigDecimal.ROUND_HALF_EVEN));
//4.35: 4.4 up
-
System.out.println(
"4.45: "+
new BigDecimal(
"4.45").setScale(
1, BigDecimal.ROUND_HALF_EVEN));
//4.45: 4.4 down
-
System.out.println(
"4.55: "+
new BigDecimal(
"4.55").setScale(
1, BigDecimal.ROUND_HALF_EVEN));
//4.55: 4.6 up
-
System.out.println(
"4.65: "+
new BigDecimal(
"4.65").setScale(
1, BigDecimal.ROUND_HALF_EVEN));
//4.65: 4.6 down
-
-
System.out.println(
"3.05: "+
new BigDecimal(
"3.05").setScale(
1, BigDecimal.ROUND_HALF_EVEN));
//3.05: 3.0 down
-
System.out.println(
"3.15: "+
new BigDecimal(
"3.15").setScale(
1, BigDecimal.ROUND_HALF_EVEN));
//3.15: 3.2 up
-
System.out.println(
"3.25: "+
new BigDecimal(
"3.25").setScale(
1, BigDecimal.ROUND_HALF_EVEN));
//3.25: 3.2 down
-
System.out.println(
"3.35: "+
new BigDecimal(
"3.35").setScale(
1, BigDecimal.ROUND_HALF_EVEN));
//3.35: 3.4 up
-
System.out.println(
"3.45: "+
new BigDecimal(
"3.45").setScale(
1, BigDecimal.ROUND_HALF_EVEN));
//3.45: 3.4 down
-
System.out.println(
"3.55: "+
new BigDecimal(
"3.55").setScale(
1, BigDecimal.ROUND_HALF_EVEN));
//3.55: 3.6 up
-
System.out.println(
"3.65: "+
new BigDecimal(
"3.65").setScale(
1, BigDecimal.ROUND_HALF_EVEN));
//3.65: 3.6 down
8.ROUND_UNNECESSARY
-
BigDecimal l =
new BigDecimal(
"2.215").setScale(
3, BigDecimal.ROUND_UNNECESSARY);
-
System.out.println(l);
-
//斷言請求的操作具有精確的結果，因此不需要舍入。
-
//如果對獲得精確結果的操作指定此舍入模式，則拋出ArithmeticException。