Java™ Platform
Standard Ed. 6

java.lang
Class Double

java.lang.Object
  extended by java.lang.Number
      extended by java.lang.Double
All Implemented Interfaces:
Serializable, Comparable<Double>

public final class Double
extends Number
implements Comparable<Double>

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 int MAX_EXPONENT
          Maximum exponent a finite double variable may have.
static double MAX_VALUE
          A constant holding the largest positive finite value of type double, (2-2-52)·21023.
static int MIN_EXPONENT
          Minimum exponent a normalized double variable may have.
static double MIN_NORMAL
          A constant holding the smallest positive normal value of type double, 2-1022.
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 int SIZE
          The number of bits used to represent a double value.
static Class<Double> 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.
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).
static String toHexString(double d)
          Returns a hexadecimal string representation of the double argument.
 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(double d)
          Returns a Double instance representing the specified double value.
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 hexadecimal floating-point literal 0x1.fffffffffffffP+1023 and also equal to Double.longBitsToDouble(0x7fefffffffffffffL).

See Also:
Constant Field Values

MIN_NORMAL

public static final double MIN_NORMAL
A constant holding the smallest positive normal value of type double, 2-1022. It is equal to the hexadecimal floating-point literal 0x1.0p-1022 and also equal to Double.longBitsToDouble(0x0010000000000000L).

Since:
1.6
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 hexadecimal floating-point literal 0x0.0000000000001P-1022 and also equal to Double.longBitsToDouble(0x1L).

See Also:
Constant Field Values

MAX_EXPONENT

public static final int MAX_EXPONENT
Maximum exponent a finite double variable may have. It is equal to the value returned by Math.getExponent(Double.MAX_VALUE).

Since:
1.6
See Also:
Constant Field Values

MIN_EXPONENT

public static final int MIN_EXPONENT
Minimum exponent a normalized double variable may have. It is equal to the value returned by Math.getExponent(Double.MIN_NORMAL).

Since:
1.6
See Also:
Constant Field Values

SIZE

public static final int SIZE
The number of bits used to represent a double value.

Since:
1.5
See Also:
Constant Field Values

TYPE

public static final Class<Double> 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. 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.

toHexString

public static String toHexString(double d)
Returns a hexadecimal string representation of the double argument. All characters mentioned below are ASCII characters.

Examples

Floating-point ValueHexadecimal String
1.0 0x1.0p0
-1.0 -0x1.0p0
2.0 0x1.0p1
3.0 0x1.8p1
0.5 0x1.0p-1
0.25 0x1.0p-2
Double.MAX_VALUE 0x1.fffffffffffffp1023
Minimum Normal Value 0x1.0p-1022
Maximum Subnormal Value 0x0.fffffffffffffp-1022
Double.MIN_VALUE 0x0.0000000000001p-1022

Parameters:
d - the double to be converted.
Returns:
a hex string representation of the argument.
Since:
1.5

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. Whitespace is removed as if by the String.trim() method; that is, both ASCII space and control characters are removed. The rest of s should constitute a FloatValue as described by the lexical syntax rules:

FloatValue:
Signopt NaN
Signopt Infinity
Signopt FloatingPointLiteral
Signopt HexFloatingPointLiteral
SignedInteger

HexFloatingPointLiteral:
HexSignificand BinaryExponent FloatTypeSuffixopt

HexSignificand:
HexNumeral
HexNumeral .
0x HexDigitsopt . HexDigits
0X HexDigitsopt . HexDigits

BinaryExponent:
BinaryExponentIndicator SignedInteger

BinaryExponentIndicator:
p
P
where Sign, FloatingPointLiteral, HexNumeral, HexDigits, SignedInteger and FloatTypeSuffix are as defined in the lexical structure sections of the 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" or as an exact hexadecimal value; this exact numerical 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.

Note that trailing format specifiers, specifiers that determine the type of a floating-point literal (1.0f is a float value; 1.0d is a double value), do not influence the results of this method. In other words, the numerical value of the input string is converted directly to the target floating-point type. The two-step sequence of conversions, string to float followed by float to double, is not equivalent to converting a string directly to double. For example, the float literal 0.1f is equal to the double value 0.10000000149011612; the float literal 0.1f represents a different numerical value than the double literal 0.1. (The numerical value 0.1 cannot be exactly represented in a binary floating-point number.)

To avoid calling this method on an invalid string and having a NumberFormatException be thrown, the regular expression below can be used to screen the input string:

        final String Digits     = "(\\p{Digit}+)";
  final String HexDigits  = "(\\p{XDigit}+)";
        // an exponent is 'e' or 'E' followed by an optionally 
        // signed decimal integer.
        final String Exp        = "[eE][+-]?"+Digits;
        final String fpRegex    =
            ("[\\x00-\\x20]*"+  // Optional leading "whitespace"
             "[+-]?(" + // Optional sign character
             "NaN|" +           // "NaN" string
             "Infinity|" +      // "Infinity" string

             // A decimal floating-point string representing a finite positive
             // number without a leading sign has at most five basic pieces:
             // Digits . Digits ExponentPart FloatTypeSuffix
             // 
             // Since this method allows integer-only strings as input
             // in addition to strings of floating-point literals, the
             // two sub-patterns below are simplifications of the grammar
             // productions from the Java Language Specification, 2nd 
             // edition, section 3.10.2.

             // Digits ._opt Digits_opt ExponentPart_opt FloatTypeSuffix_opt
             "((("+Digits+"(\\.)?("+Digits+"?)("+Exp+")?)|"+

             // . Digits ExponentPart_opt FloatTypeSuffix_opt
             "(\\.("+Digits+")("+Exp+")?)|"+

       // Hexadecimal strings
       "((" +
        // 0[xX] HexDigits ._opt BinaryExponent FloatTypeSuffix_opt
        "(0[xX]" + HexDigits + "(\\.)?)|" +

        // 0[xX] HexDigits_opt . HexDigits BinaryExponent FloatTypeSuffix_opt
        "(0[xX]" + HexDigits + "?(\\.)" + HexDigits + ")" +

        ")[pP][+-]?" + Digits + "))" +
             "[fFdD]?))" +
             "[\\x00-\\x20]*");// Optional trailing "whitespace"
            
  if (Pattern.matches(fpRegex, myString))
            Double.valueOf(myString); // Will not throw NumberFormatException
        else {
            // Perform suitable alternative action
        }
 

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.

valueOf

public static Double valueOf(double d)
Returns a Double instance representing the specified double value. If a new Double instance is not required, this method should generally be used in preference to the constructor Double(double), as this method is likely to yield significantly better space and time performance by caching frequently requested values.

Parameters:
d - a double value.
Returns:
a Double instance representing d.
Since:
1.5

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:

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.

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 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.
Since:
1.3

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·2e-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: This ensures that the natural ordering of Double objects imposed by this method is consistent with equals.

Specified by:
compareTo in interface Comparable<Double>
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

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

Java™ Platform
Standard Ed. 6

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