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RoundingMode (Java Platform SE 6) - JDK 5 Documentation v6.0, Java 2 SDK 英文文档
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Java™ Platform Standard Ed. 6 |
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java.math
Enum RoundingMode
java.lang.Objectjava.lang.Enum<RoundingMode>
- All Implemented Interfaces:
- Serializable, Comparable<RoundingMode>
public enum RoundingMode
- extends Enum<RoundingMode>
Specifies a rounding behavior for numerical operations capable of discarding precision. Each rounding mode indicates how the least significant returned digit of a rounded result is to be calculated. If fewer digits are returned than the digits needed to represent the exact numerical result, the discarded digits will be referred to as the discarded fraction regardless the digits' contribution to the value of the number. In other words, considered as a numerical value, the discarded fraction could have an absolute value greater than one.
Each rounding mode description includes a table listing how
different two-digit decimal values would round to a one digit
decimal value under the rounding mode in question. The result
column in the tables could be gotten by creating a
BigDecimal number with the specified value, forming a
MathContext object with the proper settings
(precision set to 1, and the
roundingMode set to the rounding mode in question), and
calling round on this number with the
proper MathContext. A summary table showing the results
of these rounding operations for all rounding modes appears below.
| Result of rounding input to one digit with the given rounding mode | ||||||||
|---|---|---|---|---|---|---|---|---|
| Input Number | UP | DOWN | CEILING | FLOOR | HALF_UP | HALF_DOWN | HALF_EVEN | UNNECESSARY |
| 5.5 | 6 | 5 | 6 | 5 | 6 | 5 | 6 | throw ArithmeticException |
| 2.5 | 3 | 2 | 3 | 2 | 3 | 2 | 2 | throw ArithmeticException |
| 1.6 | 2 | 1 | 2 | 1 | 2 | 2 | 2 | throw ArithmeticException |
| 1.1 | 2 | 1 | 2 | 1 | 1 | 1 | 1 | throw ArithmeticException |
| 1.0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| -1.0 | -1 | -1 | -1 | -1 | -1 | -1 | -1 | -1 |
| -1.1 | -2 | -1 | -1 | -2 | -1 | -1 | -1 | throw ArithmeticException |
| -1.6 | -2 | -1 | -1 | -2 | -2 | -2 | -2 | throw ArithmeticException |
| -2.5 | -3 | -2 | -2 | -3 | -3 | -2 | -2 | throw ArithmeticException |
| -5.5 | -6 | -5 | -5 | -6 | -6 | -5 | -6 | throw ArithmeticException |
This enum is intended to replace the integer-based
enumeration of rounding mode constants in BigDecimal
(BigDecimal.ROUND_UP, BigDecimal.ROUND_DOWN,
etc. ).
- Since:
- 1.5
- See Also:
BigDecimal,MathContext
| Enum Constant Summary | |
|---|---|
CEILING
Rounding mode to round towards positive infinity. |
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DOWN
Rounding mode to round towards zero. |
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FLOOR
Rounding mode to round towards negative infinity. |
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HALF_DOWN
Rounding mode to round towards "nearest neighbor" unless both neighbors are equidistant, in which case round down. |
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HALF_EVEN
Rounding mode to round towards the "nearest neighbor" unless both neighbors are equidistant, in which case, round towards the even neighbor. |
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HALF_UP
Rounding mode to round towards "nearest neighbor" unless both neighbors are equidistant, in which case round up. |
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UNNECESSARY
Rounding mode to assert that the requested operation has an exact result, hence no rounding is necessary. |
|
UP
Rounding mode to round away from zero. |
|
| Method Summary | |
|---|---|
static RoundingMode |
valueOf(int rm)
Returns the RoundingMode object corresponding to a legacy integer rounding mode constant in BigDecimal. |
static RoundingMode |
valueOf(String name)
Returns the enum constant of this type with the specified name. |
static RoundingMode[] |
values()
Returns an array containing the constants of this enum type, in the order they are declared. |
| Methods inherited from class java.lang.Enum |
|---|
clone, compareTo, equals, finalize, getDeclaringClass, hashCode, name, ordinal, toString, valueOf |
| Methods inherited from class java.lang.Object |
|---|
getClass, notify, notifyAll, wait, wait, wait |
| Enum Constant Detail |
|---|
UP
public static final RoundingMode UP
- Rounding mode to round away from zero. Always increments the
digit prior to a non-zero discarded fraction. Note that this
rounding mode never decreases the magnitude of the calculated
value.
Example:
Input Number Input rounded to one digit
with UP rounding5.5 6 2.5 3 1.6 2 1.1 2 1.0 1 -1.0 -1 -1.1 -2 -1.6 -2 -2.5 -3 -5.5 -6
DOWN
public static final RoundingMode DOWN
- 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.
Example:
Input Number Input rounded to one digit
with DOWN rounding5.5 5 2.5 2 1.6 1 1.1 1 1.0 1 -1.0 -1 -1.1 -1 -1.6 -1 -2.5 -2 -5.5 -5
CEILING
public static final RoundingMode CEILING
- Rounding mode to round towards positive infinity. If the
result is positive, behaves as for RoundingMode.UP;
if negative, behaves as for RoundingMode.DOWN. Note
that this rounding mode never decreases the calculated value.
Example:
Input Number Input rounded to one digit
with CEILING rounding5.5 6 2.5 3 1.6 2 1.1 2 1.0 1 -1.0 -1 -1.1 -1 -1.6 -1 -2.5 -2 -5.5 -5
FLOOR
public static final RoundingMode FLOOR
- Rounding mode to round towards negative infinity. If the
result is positive, behave as for RoundingMode.DOWN;
if negative, behave as for RoundingMode.UP. Note that
this rounding mode never increases the calculated value.
Example:
Input Number Input rounded to one digit
with FLOOR rounding5.5 5 2.5 2 1.6 1 1.1 1 1.0 1 -1.0 -1 -1.1 -2 -1.6 -2 -2.5 -3 -5.5 -6
HALF_UP
public static final RoundingMode HALF_UP
- Rounding mode to round towards "nearest neighbor"
unless both neighbors are equidistant, in which case round up.
Behaves as for RoundingMode.UP if the discarded
fraction is >= 0.5; otherwise, behaves as for
RoundingMode.DOWN. Note that this is the rounding
mode commonly taught at school.
Example:
Input Number Input rounded to one digit
with HALF_UP rounding5.5 6 2.5 3 1.6 2 1.1 1 1.0 1 -1.0 -1 -1.1 -1 -1.6 -2 -2.5 -3 -5.5 -6
HALF_DOWN
public static final RoundingMode HALF_DOWN
- Rounding mode to round towards "nearest neighbor"
unless both neighbors are equidistant, in which case round
down. Behaves as for RoundingMode.UP if the discarded
fraction is > 0.5; otherwise, behaves as for
RoundingMode.DOWN.
Example:
Input Number Input rounded to one digit
with HALF_DOWN rounding5.5 5 2.5 2 1.6 2 1.1 1 1.0 1 -1.0 -1 -1.1 -1 -1.6 -2 -2.5 -2 -5.5 -5
HALF_EVEN
public static final RoundingMode HALF_EVEN
- Rounding mode to round towards the "nearest neighbor"
unless both neighbors are equidistant, in which case, round
towards the even neighbor. Behaves as for
RoundingMode.HALF_UP if the digit to the left of the
discarded fraction is odd; behaves as for
RoundingMode.HALF_DOWN if it's even. Note that this
is the rounding mode that statistically minimizes cumulative
error when applied repeatedly over a sequence of calculations.
It is sometimes known as "Banker's rounding," and is
chiefly used in the USA. This rounding mode is analogous to
the rounding policy used for float and double
arithmetic in Java.
Example:
Input Number Input rounded to one digit
with HALF_EVEN rounding5.5 6 2.5 2 1.6 2 1.1 1 1.0 1 -1.0 -1 -1.1 -1 -1.6 -2 -2.5 -2 -5.5 -6
UNNECESSARY
public static final RoundingMode UNNECESSARY
- 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
ArithmeticException is thrown.
Example:
Input Number Input rounded to one digit
with UNNECESSARY rounding5.5 throw ArithmeticException 2.5 throw ArithmeticException 1.6 throw ArithmeticException 1.1 throw ArithmeticException 1.0 1 -1.0 -1 -1.1 throw ArithmeticException -1.6 throw ArithmeticException -2.5 throw ArithmeticException -5.5 throw ArithmeticException
| Method Detail |
|---|
values
public static RoundingMode[] values()
- Returns an array containing the constants of this enum type, in
the order they are declared. This method may be used to iterate
over the constants as follows:
for (RoundingMode c : RoundingMode.values()) System.out.println(c);
- Returns:
- an array containing the constants of this enum type, in the order they are declared
valueOf
public static RoundingMode valueOf(String name)
- Returns the enum constant of this type with the specified name.
The string must match exactly an identifier used to declare an
enum constant in this type. (Extraneous whitespace characters are
not permitted.)
- Parameters:
name- the name of the enum constant to be returned.- Returns:
- the enum constant with the specified name
- Throws:
IllegalArgumentException- if this enum type has no constant with the specified nameNullPointerException- if the argument is null
valueOf
public static RoundingMode valueOf(int rm)
- Returns the RoundingMode object corresponding to a
legacy integer rounding mode constant in
BigDecimal.- Parameters:
rm- legacy integer rounding mode to convert- Returns:
- RoundingMode corresponding to the given integer.
- Throws:
IllegalArgumentException- integer is out of range
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Java™ Platform Standard Ed. 6 |
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Submit a bug or feature
For further API reference and developer documentation, see Java SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
Copyright 2006 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.