java一个整数除以一个小数为啥的到小数

Posted 2023-02-15

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; 参考技术A java一个整数除以一个小数为什么的到小数
主要是因为java中的【简单类型】636f707962616964757a686964616f31333332643230并不适用于对【浮点】的【 精确计算】。,其它语言也存在同样的问题。