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MathContext (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
Class MathContext

java.lang.Object
  extended by java.math.MathContext
All Implemented Interfaces:
Serializable
public final class MathContext
extends Object
implements Serializable

Immutable objects which encapsulate the context settings which describe certain rules for numerical operators, such as those implemented by the BigDecimal class.

The base-independent settings are:

  1. precision: the number of digits to be used for an operation; results are rounded to this precision
  2. roundingMode: a RoundingMode object which specifies the algorithm to be used for rounding.

Since:
1.5
See Also:
BigDecimal, RoundingMode, Serialized Form

Field Summary
static MathContext DECIMAL128
          A MathContext object with a precision setting matching the IEEE 754R Decimal128 format, 34 digits, and a rounding mode of HALF_EVEN, the IEEE 754R default.
static MathContext DECIMAL32
          A MathContext object with a precision setting matching the IEEE 754R Decimal32 format, 7 digits, and a rounding mode of HALF_EVEN, the IEEE 754R default.
static MathContext DECIMAL64
          A MathContext object with a precision setting matching the IEEE 754R Decimal64 format, 16 digits, and a rounding mode of HALF_EVEN, the IEEE 754R default.
static MathContext UNLIMITED
          A MathContext object whose settings have the values required for unlimited precision arithmetic.
 
Constructor Summary
MathContext(int setPrecision)
          Constructs a new MathContext with the specified precision and the HALF_UP rounding mode.
MathContext(int setPrecision, RoundingMode setRoundingMode)
          Constructs a new MathContext with a specified precision and rounding mode.
MathContext(String val)
          Constructs a new MathContext from a string.
 
Method Summary
 boolean equals(Object x)
          Compares this MathContext with the specified Object for equality.
 int getPrecision()
          Returns the precision setting.
 RoundingMode getRoundingMode()
          Returns the roundingMode setting.
 int hashCode()
          Returns the hash code for this MathContext.
 String toString()
          Returns the string representation of this MathContext.
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
 

Field Detail

UNLIMITED

public static final MathContext UNLIMITED
A MathContext object whose settings have the values required for unlimited precision arithmetic. The values of the settings are: precision=0 roundingMode=HALF_UP

DECIMAL32

public static final MathContext DECIMAL32
A MathContext object with a precision setting matching the IEEE 754R Decimal32 format, 7 digits, and a rounding mode of HALF_EVEN, the IEEE 754R default.

DECIMAL64

public static final MathContext DECIMAL64
A MathContext object with a precision setting matching the IEEE 754R Decimal64 format, 16 digits, and a rounding mode of HALF_EVEN, the IEEE 754R default.

DECIMAL128

public static final MathContext DECIMAL128
A MathContext object with a precision setting matching the IEEE 754R Decimal128 format, 34 digits, and a rounding mode of HALF_EVEN, the IEEE 754R default.

Constructor Detail

MathContext

public MathContext(int setPrecision)
Constructs a new MathContext with the specified precision and the HALF_UP rounding mode.

Parameters:
setPrecision - The non-negative int precision setting.
Throws:
IllegalArgumentException - if the setPrecision parameter is less than zero.

MathContext

public MathContext(int setPrecision,
                   RoundingMode setRoundingMode)
Constructs a new MathContext with a specified precision and rounding mode.

Parameters:
setPrecision - The non-negative int precision setting.
setRoundingMode - The rounding mode to use.
Throws:
IllegalArgumentException - if the setPrecision parameter is less than zero.
NullPointerException - if the rounding mode argument is null

MathContext

public MathContext(String val)
Constructs a new MathContext from a string. The string must be in the same format as that produced by the toString() method.

An IllegalArgumentException is thrown if the precision section of the string is out of range (< 0) or the string is not in the format created by the toString() method.

Parameters:
val - The string to be parsed
Throws:
IllegalArgumentException - if the precision section is out of range or of incorrect format
NullPointerException - if the argument is null
Method Detail

getPrecision

public int getPrecision()
Returns the precision setting. This value is always non-negative.

Returns:
an int which is the value of the precision setting

getRoundingMode

public RoundingMode getRoundingMode()
Returns the roundingMode setting. This will be one of RoundingMode.CEILING, RoundingMode.DOWN, RoundingMode.FLOOR, RoundingMode.HALF_DOWN, RoundingMode.HALF_EVEN, RoundingMode.HALF_UP, RoundingMode.UNNECESSARY, or RoundingMode.UP.

Returns:
a RoundingMode object which is the value of the roundingMode setting

equals

public boolean equals(Object x)
Compares this MathContext with the specified Object for equality.

Overrides:
equals in class Object
Parameters:
x - Object to which this MathContext is to be compared.
Returns:
true if and only if the specified Object is a MathContext object which has exactly the same settings as this object
See Also:
Object.hashCode(), Hashtable

hashCode

public int hashCode()
Returns the hash code for this MathContext.

Overrides:
hashCode in class Object
Returns:
hash code for this MathContext
See Also:
Object.equals(java.lang.Object), Hashtable

toString

public String toString()
Returns the string representation of this MathContext. The String returned represents the settings of the MathContext object as two space-delimited words (separated by a single space character, '\u0020', and with no leading or trailing white space), as follows:
  1. The string "precision=", immediately followed by the value of the precision setting as a numeric string as if generated by the Integer.toString method.
  2. The string "roundingMode=", immediately followed by the value of the roundingMode setting as a word. This word will be the same as the name of the corresponding public constant in the RoundingMode enum.

For example: 

 precision=9 roundingMode=HALF_UP
Additional words may be appended to the result of toString in the future if more properties are added to this class.

Overrides:
toString in class Object
Returns:
a String representing the context settings
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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.