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/*
* Portions Copyright IBM Corporation, 2001. All Rights Reserved.
*/
package java.math;
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.
Summary of Rounding Operations Under Different Rounding Modes
Input Number Result of rounding input to one digit with the given
rounding mode
UPDOWNCEILINGFLOORHALF_UPHALF_DOWNHALF_EVENUNNECESSARY
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. ).
Author: Josh Bloch, Mike Cowlishaw, Joseph D. Darcy See Also: Since: 1.5
/**
* Specifies a <i>rounding behavior</i> 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 <i>discarded fraction</i> 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.
*
* <p>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
* {@code BigDecimal} number with the specified value, forming a
* {@link MathContext} object with the proper settings
* ({@code precision} set to {@code 1}, and the
* {@code roundingMode} set to the rounding mode in question), and
* calling {@link BigDecimal#round round} on this number with the
* proper {@code MathContext}. A summary table showing the results
* of these rounding operations for all rounding modes appears below.
*
*<table class="striped">
* <caption><b>Summary of Rounding Operations Under Different Rounding Modes</b></caption>
* <thead>
* <tr><th scope="col" rowspan="2">Input Number</th><th scope="col"colspan=8>Result of rounding input to one digit with the given
* rounding mode</th>
* <tr style="vertical-align:top">
* <th>{@code UP}</th>
* <th>{@code DOWN}</th>
* <th>{@code CEILING}</th>
* <th>{@code FLOOR}</th>
* <th>{@code HALF_UP}</th>
* <th>{@code HALF_DOWN}</th>
* <th>{@code HALF_EVEN}</th>
* <th>{@code UNNECESSARY}</th>
* </thead>
* <tbody style="text-align:right">
*
* <tr><th scope="row">5.5</th> <td>6</td> <td>5</td> <td>6</td> <td>5</td> <td>6</td> <td>5</td> <td>6</td> <td>throw {@code ArithmeticException}</td>
* <tr><th scope="row">2.5</th> <td>3</td> <td>2</td> <td>3</td> <td>2</td> <td>3</td> <td>2</td> <td>2</td> <td>throw {@code ArithmeticException}</td>
* <tr><th scope="row">1.6</th> <td>2</td> <td>1</td> <td>2</td> <td>1</td> <td>2</td> <td>2</td> <td>2</td> <td>throw {@code ArithmeticException}</td>
* <tr><th scope="row">1.1</th> <td>2</td> <td>1</td> <td>2</td> <td>1</td> <td>1</td> <td>1</td> <td>1</td> <td>throw {@code ArithmeticException}</td>
* <tr><th scope="row">1.0</th> <td>1</td> <td>1</td> <td>1</td> <td>1</td> <td>1</td> <td>1</td> <td>1</td> <td>1</td>
* <tr><th scope="row">-1.0</th> <td>-1</td> <td>-1</td> <td>-1</td> <td>-1</td> <td>-1</td> <td>-1</td> <td>-1</td> <td>-1</td>
* <tr><th scope="row">-1.1</th> <td>-2</td> <td>-1</td> <td>-1</td> <td>-2</td> <td>-1</td> <td>-1</td> <td>-1</td> <td>throw {@code ArithmeticException}</td>
* <tr><th scope="row">-1.6</th> <td>-2</td> <td>-1</td> <td>-1</td> <td>-2</td> <td>-2</td> <td>-2</td> <td>-2</td> <td>throw {@code ArithmeticException}</td>
* <tr><th scope="row">-2.5</th> <td>-3</td> <td>-2</td> <td>-2</td> <td>-3</td> <td>-3</td> <td>-2</td> <td>-2</td> <td>throw {@code ArithmeticException}</td>
* <tr><th scope="row">-5.5</th> <td>-6</td> <td>-5</td> <td>-5</td> <td>-6</td> <td>-6</td> <td>-5</td> <td>-6</td> <td>throw {@code ArithmeticException}</td>
* </tbody>
* </table>
*
*
* <p>This {@code enum} is intended to replace the integer-based
* enumeration of rounding mode constants in {@link BigDecimal}
* ({@link BigDecimal#ROUND_UP}, {@link BigDecimal#ROUND_DOWN},
* etc. ).
*
* @see BigDecimal
* @see MathContext
* @author Josh Bloch
* @author Mike Cowlishaw
* @author Joseph D. Darcy
* @since 1.5
*/
@SuppressWarnings("deprecation") // Legacy rounding mode constants in BigDecimal
public enum RoundingMode {
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:
Rounding mode UP Examples
Input Number
Input rounded to one digit
with UP rounding 5.5 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
/**
* 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.
*
*<p>Example:
*<table class="striped">
* <caption>Rounding mode UP Examples</caption>
*<thead>
*<tr style="vertical-align:top"><th scope="col">Input Number</th>
* <th scope="col">Input rounded to one digit<br> with {@code UP} rounding
*</thead>
*<tbody style="text-align:right">
*<tr><th scope="row">5.5</th> <td>6</td>
*<tr><th scope="row">2.5</th> <td>3</td>
*<tr><th scope="row">1.6</th> <td>2</td>
*<tr><th scope="row">1.1</th> <td>2</td>
*<tr><th scope="row">1.0</th> <td>1</td>
*<tr><th scope="row">-1.0</th> <td>-1</td>
*<tr><th scope="row">-1.1</th> <td>-2</td>
*<tr><th scope="row">-1.6</th> <td>-2</td>
*<tr><th scope="row">-2.5</th> <td>-3</td>
*<tr><th scope="row">-5.5</th> <td>-6</td>
*</tbody>
*</table>
*/
UP(BigDecimal.ROUND_UP),
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:
Rounding mode DOWN Examples
Input Number
Input rounded to one digit
with DOWN rounding 5.5 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
/**
* 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.
*
*<p>Example:
*<table class="striped">
* <caption>Rounding mode DOWN Examples</caption>
*<thead>
*<tr style="vertical-align:top"><th scope="col">Input Number</th>
* <th scope="col">Input rounded to one digit<br> with {@code DOWN} rounding
*</thead>
*<tbody style="text-align:right">
*<tr><th scope="row">5.5</th> <td>5</td>
*<tr><th scope="row">2.5</th> <td>2</td>
*<tr><th scope="row">1.6</th> <td>1</td>
*<tr><th scope="row">1.1</th> <td>1</td>
*<tr><th scope="row">1.0</th> <td>1</td>
*<tr><th scope="row">-1.0</th> <td>-1</td>
*<tr><th scope="row">-1.1</th> <td>-1</td>
*<tr><th scope="row">-1.6</th> <td>-1</td>
*<tr><th scope="row">-2.5</th> <td>-2</td>
*<tr><th scope="row">-5.5</th> <td>-5</td>
*</tbody>
*</table>
*/
DOWN(BigDecimal.ROUND_DOWN),
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:
Rounding mode CEILING Examples
Input Number
Input rounded to one digit
with CEILING rounding 5.5 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
/**
* Rounding mode to round towards positive infinity. If the
* result is positive, behaves as for {@code RoundingMode.UP};
* if negative, behaves as for {@code RoundingMode.DOWN}. Note
* that this rounding mode never decreases the calculated value.
*
*<p>Example:
*<table class="striped">
* <caption>Rounding mode CEILING Examples</caption>
*<thead>
*<tr style="vertical-align:top"><th>Input Number</th>
* <th>Input rounded to one digit<br> with {@code CEILING} rounding
*</thead>
*<tbody style="text-align:right">
*<tr><th scope="row">5.5</th> <td>6</td>
*<tr><th scope="row">2.5</th> <td>3</td>
*<tr><th scope="row">1.6</th> <td>2</td>
*<tr><th scope="row">1.1</th> <td>2</td>
*<tr><th scope="row">1.0</th> <td>1</td>
*<tr><th scope="row">-1.0</th> <td>-1</td>
*<tr><th scope="row">-1.1</th> <td>-1</td>
*<tr><th scope="row">-1.6</th> <td>-1</td>
*<tr><th scope="row">-2.5</th> <td>-2</td>
*<tr><th scope="row">-5.5</th> <td>-5</td>
*</tbody>
*</table>
*/
CEILING(BigDecimal.ROUND_CEILING),
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:
Rounding mode FLOOR Examples
Input Number
Input rounded to one digit
with FLOOR rounding 5.5 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
/**
* Rounding mode to round towards negative infinity. If the
* result is positive, behave as for {@code RoundingMode.DOWN};
* if negative, behave as for {@code RoundingMode.UP}. Note that
* this rounding mode never increases the calculated value.
*
*<p>Example:
*<table class="striped">
* <caption>Rounding mode FLOOR Examples</caption>
*<thead>
*<tr style="vertical-align:top"><th scope="col">Input Number</th>
* <th scope="col">Input rounded to one digit<br> with {@code FLOOR} rounding
*</thead>
*<tbody style="text-align:right">
*<tr><th scope="row">5.5</th> <td>5</td>
*<tr><th scope="row">2.5</th> <td>2</td>
*<tr><th scope="row">1.6</th> <td>1</td>
*<tr><th scope="row">1.1</th> <td>1</td>
*<tr><th scope="row">1.0</th> <td>1</td>
*<tr><th scope="row">-1.0</th> <td>-1</td>
*<tr><th scope="row">-1.1</th> <td>-2</td>
*<tr><th scope="row">-1.6</th> <td>-2</td>
*<tr><th scope="row">-2.5</th> <td>-3</td>
*<tr><th scope="row">-5.5</th> <td>-6</td>
*</tbody>
*</table>
*/
FLOOR(BigDecimal.ROUND_FLOOR),
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:
Rounding mode HALF_UP Examples
Input Number
Input rounded to one digit
with HALF_UP rounding 5.5 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
/**
* Rounding mode to round towards {@literal "nearest neighbor"}
* unless both neighbors are equidistant, in which case round up.
* Behaves as for {@code RoundingMode.UP} if the discarded
* fraction is ≥ 0.5; otherwise, behaves as for
* {@code RoundingMode.DOWN}. Note that this is the rounding
* mode commonly taught at school.
*
*<p>Example:
*<table class="striped">
* <caption>Rounding mode HALF_UP Examples</caption>
*<thead>
*<tr style="vertical-align:top"><th scope="col">Input Number</th>
* <th scope="col">Input rounded to one digit<br> with {@code HALF_UP} rounding
*</thead>
*<tbody style="text-align:right">
*<tr><th scope="row">5.5</th> <td>6</td>
*<tr><th scope="row">2.5</th> <td>3</td>
*<tr><th scope="row">1.6</th> <td>2</td>
*<tr><th scope="row">1.1</th> <td>1</td>
*<tr><th scope="row">1.0</th> <td>1</td>
*<tr><th scope="row">-1.0</th> <td>-1</td>
*<tr><th scope="row">-1.1</th> <td>-1</td>
*<tr><th scope="row">-1.6</th> <td>-2</td>
*<tr><th scope="row">-2.5</th> <td>-3</td>
*<tr><th scope="row">-5.5</th> <td>-6</td>
*</tbody>
*</table>
*/
HALF_UP(BigDecimal.ROUND_HALF_UP),
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:
Rounding mode HALF_DOWN Examples
Input Number
Input rounded to one digit
with HALF_DOWN rounding 5.5 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
/**
* Rounding mode to round towards {@literal "nearest neighbor"}
* unless both neighbors are equidistant, in which case round
* down. Behaves as for {@code RoundingMode.UP} if the discarded
* fraction is > 0.5; otherwise, behaves as for
* {@code RoundingMode.DOWN}.
*
*<p>Example:
*<table class="striped">
* <caption>Rounding mode HALF_DOWN Examples</caption>
*<thead>
*<tr style="vertical-align:top"><th scope="col">Input Number</th>
* <th scope="col">Input rounded to one digit<br> with {@code HALF_DOWN} rounding
*</thead>
*<tbody style="text-align:right">
*<tr><th scope="row">5.5</th> <td>5</td>
*<tr><th scope="row">2.5</th> <td>2</td>
*<tr><th scope="row">1.6</th> <td>2</td>
*<tr><th scope="row">1.1</th> <td>1</td>
*<tr><th scope="row">1.0</th> <td>1</td>
*<tr><th scope="row">-1.0</th> <td>-1</td>
*<tr><th scope="row">-1.1</th> <td>-1</td>
*<tr><th scope="row">-1.6</th> <td>-2</td>
*<tr><th scope="row">-2.5</th> <td>-2</td>
*<tr><th scope="row">-5.5</th> <td>-5</td>
*</tbody>
*</table>
*/
HALF_DOWN(BigDecimal.ROUND_HALF_DOWN),
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:
Rounding mode HALF_EVEN Examples
Input Number
Input rounded to one digit
with HALF_EVEN rounding 5.5 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
/**
* 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 RoundingMode.HALF_UP} if the digit to the left of the
* discarded fraction is odd; behaves as for
* {@code 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 {@literal "Banker's rounding,"} and is
* chiefly used in the USA. This rounding mode is analogous to
* the rounding policy used for {@code float} and {@code double}
* arithmetic in Java.
*
*<p>Example:
*<table class="striped">
* <caption>Rounding mode HALF_EVEN Examples</caption>
*<thead>
*<tr style="vertical-align:top"><th scope="col">Input Number</th>
* <th scope="col">Input rounded to one digit<br> with {@code HALF_EVEN} rounding
*</thead>
*<tbody style="text-align:right">
*<tr><th scope="row">5.5</th> <td>6</td>
*<tr><th scope="row">2.5</th> <td>2</td>
*<tr><th scope="row">1.6</th> <td>2</td>
*<tr><th scope="row">1.1</th> <td>1</td>
*<tr><th scope="row">1.0</th> <td>1</td>
*<tr><th scope="row">-1.0</th> <td>-1</td>
*<tr><th scope="row">-1.1</th> <td>-1</td>
*<tr><th scope="row">-1.6</th> <td>-2</td>
*<tr><th scope="row">-2.5</th> <td>-2</td>
*<tr><th scope="row">-5.5</th> <td>-6</td>
*</tbody>
*</table>
*/
HALF_EVEN(BigDecimal.ROUND_HALF_EVEN),
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:
Rounding mode UNNECESSARY Examples
Input Number
Input rounded to one digit
with UNNECESSARY rounding 5.5 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
/**
* 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.
*<p>Example:
*<table class="striped">
* <caption>Rounding mode UNNECESSARY Examples</caption>
*<thead>
*<tr style="vertical-align:top"><th scope="col">Input Number</th>
* <th scope="col">Input rounded to one digit<br> with {@code UNNECESSARY} rounding
*</thead>
*<tbody style="text-align:right">
*<tr><th scope="row">5.5</th> <td>throw {@code ArithmeticException}</td>
*<tr><th scope="row">2.5</th> <td>throw {@code ArithmeticException}</td>
*<tr><th scope="row">1.6</th> <td>throw {@code ArithmeticException}</td>
*<tr><th scope="row">1.1</th> <td>throw {@code ArithmeticException}</td>
*<tr><th scope="row">1.0</th> <td>1</td>
*<tr><th scope="row">-1.0</th> <td>-1</td>
*<tr><th scope="row">-1.1</th> <td>throw {@code ArithmeticException}</td>
*<tr><th scope="row">-1.6</th> <td>throw {@code ArithmeticException}</td>
*<tr><th scope="row">-2.5</th> <td>throw {@code ArithmeticException}</td>
*<tr><th scope="row">-5.5</th> <td>throw {@code ArithmeticException}</td>
*</tbody>
*</table>
*/
UNNECESSARY(BigDecimal.ROUND_UNNECESSARY);
// Corresponding BigDecimal rounding constant
final int oldMode;
Constructor
Params: - oldMode – The
BigDecimal constant corresponding to this mode
/**
* Constructor
*
* @param oldMode The {@code BigDecimal} constant corresponding to
* this mode
*/
private RoundingMode(int oldMode) {
this.oldMode = oldMode;
}
Returns the RoundingMode object corresponding to a legacy integer rounding mode constant in BigDecimal. Params: - rm – legacy integer rounding mode to convert
Throws: - IllegalArgumentException – integer is out of range
Returns: RoundingMode corresponding to the given integer.
/**
* Returns the {@code RoundingMode} object corresponding to a
* legacy integer rounding mode constant in {@link BigDecimal}.
*
* @param rm legacy integer rounding mode to convert
* @return {@code RoundingMode} corresponding to the given integer.
* @throws IllegalArgumentException integer is out of range
*/
public static RoundingMode valueOf(int rm) {
switch(rm) {
case BigDecimal.ROUND_UP:
return UP;
case BigDecimal.ROUND_DOWN:
return DOWN;
case BigDecimal.ROUND_CEILING:
return CEILING;
case BigDecimal.ROUND_FLOOR:
return FLOOR;
case BigDecimal.ROUND_HALF_UP:
return HALF_UP;
case BigDecimal.ROUND_HALF_DOWN:
return HALF_DOWN;
case BigDecimal.ROUND_HALF_EVEN:
return HALF_EVEN;
case BigDecimal.ROUND_UNNECESSARY:
return UNNECESSARY;
default:
throw new IllegalArgumentException("argument out of range");
}
}
}