Double (Java 2 Platform SE v1.4.1) - JDK 5 Documentation v1.4.1, Java 2 SDK 英文文档

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java.lang
Class Double

java.lang.Object
  |
  +--java.lang.Number
        |
        +--java.lang.Double

All Implemented Interfaces:: Comparable, Serializable

public final class Double
extends Number
implements Comparable

The Double class wraps a value of the primitive type double in an object. An object of type Double contains a single field whose type is double.

In addition, this class provides several methods for converting a double to a String and a String to a double, as well as other constants and methods useful when dealing with a double.

Since:: JDK1.0
See Also:: Serialized Form

Field Summary

static double MAX_VALUE
          A constant holding the largest positive finite value of type double, (2-2^-52)·2¹⁰²³.

static double MIN_VALUE
          A constant holding the smallest positive nonzero value of type double, 2^-1074.

static double NaN
          A constant holding a Not-a-Number (NaN) value of type double.

static double NEGATIVE_INFINITY
          A constant holding the negative infinity of type double.

static double POSITIVE_INFINITY
          A constant holding the positive infinity of type double.

static Class TYPE
          The Class instance representing the primitive type double.

Constructor Summary

Double(double value)
          Constructs a newly allocated Double object that represents the primitive double argument.

Double(String s)
          Constructs a newly allocated Double object that represents the floating-point value of type double represented by the string.

Method Summary

byte byteValue()
          Returns the value of this Double as a byte (by casting to a byte).

static int compare(double d1, double d2)
          Compares the two specified double values.

int compareTo(Double anotherDouble)
          Compares two Double objects numerically.

int compareTo(Object o)
          Compares this Double object to another object.

static long doubleToLongBits(double value)
          Returns a representation of the specified floating-point value according to the IEEE 754 floating-point "double format" bit layout.

static long doubleToRawLongBits(double value)
          Returns a representation of the specified floating-point value according to the IEEE 754 floating-point "double format" bit layout, preserving Not-a-Number (NaN) values.

double doubleValue()
          Returns the double value of this Double object.

boolean equals(Object obj)
          Compares this object against the specified object.

float floatValue()
          Returns the float value of this Double object.

int hashCode()
          Returns a hash code for this Double object.

int intValue()
          Returns the value of this Double as an int (by casting to type int).

boolean isInfinite()
          Returns true if this Double value is infinitely large in magnitude, false otherwise.

static boolean isInfinite(double v)
          Returns true if the specified number is infinitely large in magnitude, false otherwise.

boolean isNaN()
          Returns true if this Double value is a Not-a-Number (NaN), false otherwise.

static boolean isNaN(double v)
          Returns true if the specified number is a Not-a-Number (NaN) value, false otherwise.

static double longBitsToDouble(long bits)
          Returns the double value corresponding to a given bit representation.

long longValue()
          Returns the value of this Double as a long (by casting to type long).

static double parseDouble(String s)
          Returns a new double initialized to the value represented by the specified String, as performed by the valueOf method of class Double.

short shortValue()
          Returns the value of this Double as a short (by casting to a short).

String toString()
          Returns a string representation of this Double object.

static String toString(double d)
          Returns a string representation of the double argument.

static Double valueOf(String s)
          Returns a Double object holding the double value represented by the argument string s.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

POSITIVE_INFINITY

public static final double POSITIVE_INFINITY

A constant holding the positive infinity of type double. It is equal to the value returned by Double.longBitsToDouble(0x7ff0000000000000L).

See Also:: Constant Field Values

NEGATIVE_INFINITY

public static final double NEGATIVE_INFINITY

A constant holding the negative infinity of type double. It is equal to the value returned by Double.longBitsToDouble(0xfff0000000000000L).

See Also:: Constant Field Values

NaN

public static final double NaN

A constant holding a Not-a-Number (NaN) value of type double. It is equivalent to the value returned by Double.longBitsToDouble(0x7ff8000000000000L).

See Also:: Constant Field Values

MAX_VALUE

public static final double MAX_VALUE

A constant holding the largest positive finite value of type double, (2-2^-52)·2¹⁰²³. It is equal to the value returned by: Double.longBitsToDouble(0x7fefffffffffffffL).

See Also:: Constant Field Values

MIN_VALUE

public static final double MIN_VALUE

A constant holding the smallest positive nonzero value of type double, 2^-1074. It is equal to the value returned by Double.longBitsToDouble(0x1L).

See Also:: Constant Field Values

TYPE

public static final Class TYPE

The Class instance representing the primitive type double.

Since:: JDK1.1

Constructor Detail

Double

public Double(double value)

Constructs a newly allocated Double object that represents the primitive double argument.
Parameters:: value - the value to be represented by the Double.

Double

public Double(String s)
       throws NumberFormatException

Constructs a newly allocated Double object that represents the floating-point value of type double represented by the string. The string is converted to a double value as if by the valueOf method.
Parameters:: s - a string to be converted to a Double.
Throws:: NumberFormatException - if the string does not contain a parsable number.
See Also:: valueOf(java.lang.String)

Method Detail

toString

public static String toString(double d)

Returns a string representation of the double argument. All characters mentioned below are ASCII characters.

If the argument is NaN, the result is the string "NaN".
Otherwise, the result is a string that represents the sign and magnitude (absolute value) of the argument. If the sign is negative, the first character of the result is '-' ('\u002D'); if the sign is positive, no sign character appears in the result. As for the magnitude m:
- If m is infinity, it is represented by the characters "Infinity"; thus, positive infinity produces the result "Infinity" and negative infinity produces the result "-Infinity".
- If m is zero, it is represented by the characters "0.0"; thus, negative zero produces the result "-0.0" and positive zero produces the result "0.0".
- If m is greater than or equal to 10^-3 but less than 10⁷, then it is represented as the integer part of m, in decimal form with no leading zeroes, followed by '.' ('\u002E'), followed by one or more decimal digits representing the fractional part of m.
- If m is less than 10^-3 or greater than or equal to 10⁷, then it is represented in so-called "computerized scientific notation." Let n be the unique integer such that 10ⁿ <= m < 10ⁿ⁺¹; then let a be the mathematically exact quotient of m and 10ⁿ so that 1 <= a < 10. The magnitude is then represented as the integer part of a, as a single decimal digit, followed by '.' ('\u002E'), followed by decimal digits representing the fractional part of a, followed by the letter 'E' ('\u0045'), followed by a representation of n as a decimal integer, as produced by the method Integer.toString(int).

How many digits must be printed for the fractional part of m or a? There must be at least one digit to represent the fractional part, and beyond that as many, but only as many, more digits as are needed to uniquely distinguish the argument value from adjacent values of type double. That is, suppose that x is the exact mathematical value represented by the decimal representation produced by this method for a finite nonzero argument d. Then d must be the double value nearest to x; or if two double values are equally close to x, then d must be one of them and the least significant bit of the significand of d must be 0.

To create localized string representations of a floating-point value, use subclasses of NumberFormat.

Parameters:: d - the double to be converted.
Returns:: a string representation of the argument.

valueOf

public static Double valueOf(String s)
                      throws NumberFormatException

Returns a Double object holding the double value represented by the argument string s.

If s is null, then a NullPointerException is thrown.

Leading and trailing whitespace characters in s are ignored. The rest of s should constitute a FloatValue as described by the lexical rule:

FloatValue:
Sign_opt NaN
Sign_opt Infinity
Sign_opt FloatingPointLiteral

where Sign and FloatingPointLiteral are as defined in §3.10.2 of the Java Language Specification. If s does not have the form of a FloatValue, then a NumberFormatException is thrown. Otherwise, s is regarded as representing an exact decimal value in the usual "computerized scientific notation"; this exact decimal value is then conceptually converted to an "infinitely precise" binary value that is then rounded to type double by the usual round-to-nearest rule of IEEE 754 floating-point arithmetic, which includes preserving the sign of a zero value. Finally, a Double object representing this double value is returned.

To interpret localized string representations of a floating-point value, use subclasses of NumberFormat.

Parameters:: s - the string to be parsed.
Returns:: a Double object holding the value represented by the String argument.
Throws:: NumberFormatException - if the string does not contain a parsable number.

parseDouble

public static double parseDouble(String s)
                          throws NumberFormatException

Returns a new double initialized to the value represented by the specified String, as performed by the valueOf method of class Double.

Parameters:: s - the string to be parsed.
Returns:: the double value represented by the string argument.
Throws:: NumberFormatException - if the string does not contain a parsable double.
Since:: 1.2
See Also:: valueOf(String)

isNaN

public static boolean isNaN(double v)

Returns true if the specified number is a Not-a-Number (NaN) value, false otherwise.

Parameters:: v - the value to be tested.
Returns:: true if the value of the argument is NaN; false otherwise.

isInfinite

public static boolean isInfinite(double v)

Returns true if the specified number is infinitely large in magnitude, false otherwise.

Parameters:: v - the value to be tested.
Returns:: true if the value of the argument is positive infinity or negative infinity; false otherwise.

isNaN

public boolean isNaN()

Returns true if this Double value is a Not-a-Number (NaN), false otherwise.

Returns:: true if the value represented by this object is NaN; false otherwise.

isInfinite

public boolean isInfinite()

Returns true if this Double value is infinitely large in magnitude, false otherwise.

Returns:: true if the value represented by this object is positive infinity or negative infinity; false otherwise.

toString

public String toString()

Returns a string representation of this Double object. The primitive double value represented by this object is converted to a string exactly as if by the method toString of one argument.

Overrides:: toString in class Object

Returns:: a String representation of this object.
See Also:: toString(double)

byteValue

public byte byteValue()

Returns the value of this Double as a byte (by casting to a byte).

Overrides:: byteValue in class Number

Returns:: the double value represented by this object converted to type byte
Since:: JDK1.1

shortValue

public short shortValue()

Returns the value of this Double as a short (by casting to a short).

Overrides:: shortValue in class Number

Returns:: the double value represented by this object converted to type short
Since:: JDK1.1

intValue

public int intValue()

Returns the value of this Double as an int (by casting to type int).

Specified by:: intValue in class Number

Returns:: the double value represented by this object converted to type int

longValue

public long longValue()

Returns the value of this Double as a long (by casting to type long).

Specified by:: longValue in class Number

Returns:: the double value represented by this object converted to type long

floatValue

public float floatValue()

Returns the float value of this Double object.

Specified by:: floatValue in class Number

Returns:: the double value represented by this object converted to type float
Since:: JDK1.0

doubleValue

public double doubleValue()

Returns the double value of this Double object.

Specified by:: doubleValue in class Number

Returns:: the double value represented by this object

hashCode

public int hashCode()

Returns a hash code for this Double object. The result is the exclusive OR of the two halves of the long integer bit representation, exactly as produced by the method doubleToLongBits(double), of the primitive double value represented by this Double object. That is, the hash code is the value of the expression:

 (int)(v^(v>>>32))

where v is defined by:

 long v = Double.doubleToLongBits(this.doubleValue());

Overrides:: hashCode in class Object

Returns:: a hash code value for this object.
See Also:: Object.equals(java.lang.Object), Hashtable

equals

public boolean equals(Object obj)

Compares this object against the specified object. The result is true if and only if the argument is not null and is a Double object that represents a double that has the same value as the double represented by this object. For this purpose, two double values are considered to be the same if and only if the method doubleToLongBits(double) returns the identical long value when applied to each.

Note that in most cases, for two instances of class Double, d1 and d2, the value of d1.equals(d2) is true if and only if

   d1.doubleValue() == d2.doubleValue()

also has the value true. However, there are two exceptions:

If d1 and d2 both represent Double.NaN, then the equals method returns true, even though Double.NaN==Double.NaN has the value false.
If d1 represents +0.0 while d2 represents -0.0, or vice versa, the equal test has the value false, even though +0.0==-0.0 has the value true.

This definition allows hash tables to operate properly.

Overrides:: equals in class Object

Parameters:: obj - the object to compare with.
Returns:: true if the objects are the same; false otherwise.
See Also:: doubleToLongBits(double)

doubleToLongBits

public static long doubleToLongBits(double value)

Returns a representation of the specified floating-point value according to the IEEE 754 floating-point "double format" bit layout.

Bit 63 (the bit that is selected by the mask 0x8000000000000000L) represents the sign of the floating-point number. Bits 62-52 (the bits that are selected by the mask 0x7ff0000000000000L) represent the exponent. Bits 51-0 (the bits that are selected by the mask 0x000fffffffffffffL) represent the significand (sometimes called the mantissa) of the floating-point number.

If the argument is positive infinity, the result is 0x7ff0000000000000L.

If the argument is negative infinity, the result is 0xfff0000000000000L.

If the argument is NaN, the result is 0x7ff8000000000000L.

In all cases, the result is a long integer that, when given to the longBitsToDouble(long) method, will produce a floating-point value the same as the argument to doubleToLongBits (except all NaN values are collapsed to a single "canonical" NaN value).

Parameters:: value - a double precision floating-point number.
Returns:: the bits that represent the floating-point number.

doubleToRawLongBits

public static long doubleToRawLongBits(double value)

Returns a representation of the specified floating-point value according to the IEEE 754 floating-point "double format" bit layout, preserving Not-a-Number (NaN) values.

If the argument is positive infinity, the result is 0x7ff0000000000000L.

If the argument is negative infinity, the result is 0xfff0000000000000L.

If the argument is NaN, the result is the long integer representing the actual NaN value. Unlike the doubleToLongBits method, doubleToRawLongBits does not collapse all the bit patterns encoding a NaN to a single "canonical" NaN value.

In all cases, the result is a long integer that, when given to the longBitsToDouble(long) method, will produce a floating-point value the same as the argument to doubleToRawLongBits.

Parameters:: value - a double precision floating-point number.
Returns:: the bits that represent the floating-point number.

longBitsToDouble

public static double longBitsToDouble(long bits)

Returns the double value corresponding to a given bit representation. The argument is considered to be a representation of a floating-point value according to the IEEE 754 floating-point "double format" bit layout.

If the argument is 0x7ff0000000000000L, the result is positive infinity.

If the argument is 0xfff0000000000000L, the result is negative infinity.

If the argument is any value in the range 0x7ff0000000000001L through 0x7fffffffffffffffL or in the range 0xfff0000000000001L through 0xffffffffffffffffL, the result is a NaN. No IEEE 754 floating-point operation provided by Java can distinguish between two NaN values of the same type with different bit patterns. Distinct values of NaN are only distinguishable by use of the Double.doubleToRawLongBits method.

In all other cases, let s, e, and m be three values that can be computed from the argument:

 int s = ((bits >> 63) == 0) ? 1 : -1;
 int e = (int)((bits >> 52) & 0x7ffL);
 long m = (e == 0) ?
                 (bits & 0xfffffffffffffL) << 1 :
                 (bits & 0xfffffffffffffL) | 0x10000000000000L;

Then the floating-point result equals the value of the mathematical expression s·m·2^e-1075.

Note that this method may not be able to return a double NaN with exactly same bit pattern as the long argument. IEEE 754 distinguishes between two kinds of NaNs, quiet NaNs and signaling NaNs. The differences between the two kinds of NaN are generally not visible in Java. Arithmetic operations on signaling NaNs turn them into quiet NaNs with a different, but often similar, bit pattern. However, on some processors merely copying a signaling NaN also performs that conversion. In particular, copying a signaling NaN to return it to the calling method may perform this conversion. So longBitsToDouble may not be able to return a double with a signaling NaN bit pattern. Consequently, for some long values, doubleToRawLongBits(longBitsToDouble(start)) may not equal start. Moreover, which particular bit patterns represent signaling NaNs is platform dependent; although all NaN bit patterns, quiet or signaling, must be in the NaN range identified above.

Parameters:: bits - any long integer.
Returns:: the double floating-point value with the same bit pattern.

compareTo

public int compareTo(Double anotherDouble)

Compares two Double objects numerically. There are two ways in which comparisons performed by this method differ from those performed by the Java language numerical comparison operators (<, <=, ==, >= >) when applied to primitive double values:

Double.NaN is considered by this method to be equal to itself and greater than all other double values (including Double.POSITIVE_INFINITY).
0.0d is considered by this method to be greater than -0.0d.

This ensures that Double.compareTo(Object) (which forwards its behavior to this method) obeys the general contract for Comparable.compareTo, and that the natural order on Doubles is consistent with equals.

Parameters:: anotherDouble - the Double to be compared.
Returns:: the value 0 if anotherDouble is numerically equal to this Double; a value less than 0 if this Double is numerically less than anotherDouble; and a value greater than 0 if this Double is numerically greater than anotherDouble.
Since:: 1.2
See Also:: Comparable.compareTo(Object)

compareTo

public int compareTo(Object o)

Compares this Double object to another object. If the object is a Double, this function behaves like compareTo(Double). Otherwise, it throws a ClassCastException (as Double objects are comparable only to other Double objects).

Specified by:: compareTo in interface Comparable

Parameters:: o - the Object to be compared.
Returns:: the value 0 if the argument is a Double numerically equal to this Double; a value less than 0 if the argument is a Double numerically greater than this Double; and a value greater than 0 if the argument is a Double numerically less than this Double.
Throws:: ClassCastException - if the argument is not a Double.
Since:: 1.2
See Also:: Comparable

compare

public static int compare(double d1,
                          double d2)

Compares the two specified double values. The sign of the integer value returned is the same as that of the integer that would be returned by the call:

    new Double(d1).compareTo(new Double(d2))

Parameters:: d1 - the first double to compare; d2 - the second double to compare
Returns:: the value 0 if d1 is numerically equal to d2; a value less than 0 if d1 is numerically less than d2; and a value greater than 0 if d1 is numerically greater than d2.
Since:: 1.4

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For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

Field Summary
`static double`	`MAX_VALUE` A constant holding the largest positive finite value of type `double`, (2-2^-52)·2¹⁰²³.
`static double`	`MIN_VALUE` A constant holding the smallest positive nonzero value of type `double`, 2^-1074.
`static double`	`NaN` A constant holding a Not-a-Number (NaN) value of type `double`.
`static double`	`NEGATIVE_INFINITY` A constant holding the negative infinity of type `double`.
`static double`	`POSITIVE_INFINITY` A constant holding the positive infinity of type `double`.
`static Class`	`TYPE` The `Class` instance representing the primitive type `double`.

Constructor Summary
`Double(double value)` Constructs a newly allocated `Double` object that represents the primitive `double` argument.
`Double(String s)` Constructs a newly allocated `Double` object that represents the floating-point value of type `double` represented by the string.

Method Summary
`byte`	`byteValue()` Returns the value of this `Double` as a `byte` (by casting to a `byte`).
`static int`	`compare(double d1, double d2)` Compares the two specified `double` values.
`int`	`compareTo(Double anotherDouble)` Compares two `Double` objects numerically.
`int`	`compareTo(Object o)` Compares this `Double` object to another object.
`static long`	`doubleToLongBits(double value)` Returns a representation of the specified floating-point value according to the IEEE 754 floating-point "double format" bit layout.
`static long`	`doubleToRawLongBits(double value)` Returns a representation of the specified floating-point value according to the IEEE 754 floating-point "double format" bit layout, preserving Not-a-Number (NaN) values.
`double`	`doubleValue()` Returns the `double` value of this `Double` object.
`boolean`	`equals(Object obj)` Compares this object against the specified object.
`float`	`floatValue()` Returns the `float` value of this `Double` object.
`int`	`hashCode()` Returns a hash code for this `Double` object.
`int`	`intValue()` Returns the value of this `Double` as an `int` (by casting to type `int`).
`boolean`	`isInfinite()` Returns `true` if this `Double` value is infinitely large in magnitude, `false` otherwise.
`static boolean`	`isInfinite(double v)` Returns `true` if the specified number is infinitely large in magnitude, `false` otherwise.
`boolean`	`isNaN()` Returns `true` if this `Double` value is a Not-a-Number (NaN), `false` otherwise.
`static boolean`	`isNaN(double v)` Returns `true` if the specified number is a Not-a-Number (NaN) value, `false` otherwise.
`static double`	`longBitsToDouble(long bits)` Returns the `double` value corresponding to a given bit representation.
`long`	`longValue()` Returns the value of this `Double` as a `long` (by casting to type `long`).
`static double`	`parseDouble(String s)` Returns a new `double` initialized to the value represented by the specified `String`, as performed by the `valueOf` method of class `Double`.
`short`	`shortValue()` Returns the value of this `Double` as a `short` (by casting to a `short`).
`String`	`toString()` Returns a string representation of this `Double` object.
`static String`	`toString(double d)` Returns a string representation of the `double` argument.
`static Double`	`valueOf(String s)` Returns a `Double` object holding the `double` value represented by the argument string `s`.

Double (Java 2 Platform SE v1.4.1) - JDK 5 Documentation v1.4.1, Java 2 SDK 英文文档

java.lang Class Double

POSITIVE_INFINITY

NEGATIVE_INFINITY

NaN

MAX_VALUE

MIN_VALUE

TYPE

Double

Double

toString

valueOf

parseDouble

isNaN

isInfinite

isNaN

isInfinite

toString

byteValue

shortValue

intValue

longValue

floatValue

doubleValue

hashCode

equals

doubleToLongBits

doubleToRawLongBits

longBitsToDouble

compareTo

compareTo

compare

java.lang
Class Double