在Java中如果除运算符“/”,在不加任何限制的情况下,两个整数相除,得到的是整数,小数点后的被舍弃。但是有些场景下我们需要拿到除得的小数,还要指定位数的小数。这时候有以下处理方法:
1.使用DecimalFormat来限定得到的小数位数
int pcm = 98;
int fcm = 11;
DecimalFormat df = new DecimalFormat("0.00");
double tmpVal = Double.parseDouble(df.format((double) pcm/(pcm+fcm)));
//get value 0.89
注意,它默认返回的是String,如果需要double/float要做一下转换。
2.直接使用Decimal运算
@Test
public void testDecimalOper(){
int pcm = 94;
int fcm = 11;
BigDecimal pcmbd = new BigDecimal(pcm);
BigDecimal fcmbd = new BigDecimal(fcm);
BigDecimal rate = new BigDecimal(0.00);
rate = pcmbd.divide(pcmbd.add(fcmbd), 2, RoundingMode.HALF_UP);
System.out.println(rate);//0.90
}
float/double在工程运算中使用的比较多,在商业计算中使用Decimal类型的比较多。(注:
在《Effective Java》这本书中也提到这个原则,float和double只能用来做科学计算或者是工程计算,在商业计算中我们要用 java.math.BigDecimal,另外,我们如果需要精确计算,要用String来够造BigDecimal。在《Effective Java》一书中的例子是用String来够造BigDecimal的。(注意:divide方法中推荐使用枚举RoundingMode.HALF_UP)
)
两种方式都可以。推荐使用第二种方式来处理精度和round mode的设置。
附BigDecimal rouding mode:
/** * Rounding mode to round away from zero. Always increments the * digit prior to a nonzero discarded fraction. Note that this rounding * mode never decreases the magnitude of the calculated value. */ public final static int ROUND_UP = 0; /** * Rounding mode to round towards zero. Never increments the digit * prior to a discarded fraction (i.e., truncates). Note that this * rounding mode never increases the magnitude of the calculated value. */ public final static int ROUND_DOWN = 1; /** * Rounding mode to round towards positive infinity. If the * {@code BigDecimal} is positive, behaves as for * {@code ROUND_UP}; if negative, behaves as for * {@code ROUND_DOWN}. Note that this rounding mode never * decreases the calculated value. */ public final static int ROUND_CEILING = 2; /** * Rounding mode to round towards negative infinity. If the * {@code BigDecimal} is positive, behave as for * {@code ROUND_DOWN}; if negative, behave as for * {@code ROUND_UP}. Note that this rounding mode never * increases the calculated value. */ public final static int ROUND_FLOOR = 3; /** * Rounding mode to round towards {@literal "nearest neighbor"} * unless both neighbors are equidistant, in which case round up. * Behaves as for {@code ROUND_UP} if the discarded fraction is * ≥ 0.5; otherwise, behaves as for {@code ROUND_DOWN}. Note * that this is the rounding mode that most of us were taught in * grade school. */ public final static int ROUND_HALF_UP = 4; /** * Rounding mode to round towards {@literal "nearest neighbor"} * unless both neighbors are equidistant, in which case round * down. Behaves as for {@code ROUND_UP} if the discarded * fraction is {@literal >} 0.5; otherwise, behaves as for * {@code ROUND_DOWN}. */ public final static int ROUND_HALF_DOWN = 5; /** * Rounding mode to round towards the {@literal "nearest neighbor"} * unless both neighbors are equidistant, in which case, round * towards the even neighbor. Behaves as for * {@code ROUND_HALF_UP} if the digit to the left of the * discarded fraction is odd; behaves as for * {@code ROUND_HALF_DOWN} if it's even. Note that this is the * rounding mode that minimizes cumulative error when applied * repeatedly over a sequence of calculations. */ public final static int ROUND_HALF_EVEN = 6; /** * Rounding mode to assert that the requested operation has an exact * result, hence no rounding is necessary. If this rounding mode is * specified on an operation that yields an inexact result, an * {@code ArithmeticException} is thrown. */ public final static int ROUND_UNNECESSARY = 7;