Class Double

java.lang.Object
java.lang.Number
java.lang.Double
All Implemented Interfaces:
Serializable, Comparable<Double>, Constable, ConstantDesc
public final class Double extends Number implements Comparable<Double>, Constable, ConstantDesc
The Double class is the wrapper class for values of the primitive type double. 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.

This is a value-based class; programmers should treat instances that are equal as interchangeable and should not use instances for synchronization, or unpredictable behavior may occur. For example, in a future release, synchronization may fail.

Floating-point Equality, Equivalence, and Comparison

IEEE 754 floating-point values include finite nonzero values, signed zeros (+0.0 and -0.0), signed infinities (positive infinity and negative infinity), and NaN (not-a-number).

An equivalence relation on a set of values is a boolean relation on pairs of values that is reflexive, symmetric, and transitive. For more discussion of equivalence relations and object equality, see the Object.equals specification. An equivalence relation partitions the values it operates over into sets called equivalence classes. All the members of the equivalence class are equal to each other under the relation. An equivalence class may contain only a single member. At least for some purposes, all the members of an equivalence class are substitutable for each other. In particular, in a numeric expression equivalent values can be substituted for one another without changing the result of the expression, meaning changing the equivalence class of the result of the expression.

Notably, the built-in == operation on floating-point values is not an equivalence relation. Despite not defining an equivalence relation, the semantics of the IEEE 754 == operator were deliberately designed to meet other needs of numerical computation. There are two exceptions where the properties of an equivalence relation are not satisfied by == on floating-point values:

  • If v1 and v2 are both NaN, then v1 == v2 has the value false. Therefore, for two NaN arguments the reflexive property of an equivalence relation is not satisfied by the == operator.
  • If v1 represents +0.0 while v2 represents -0.0, or vice versa, then v1 == v2 has the value true even though +0.0 and -0.0 are distinguishable under various floating-point operations. For example, 1.0/+0.0 evaluates to positive infinity while 1.0/-0.0 evaluates to negative infinity and positive infinity and negative infinity are neither equal to each other nor equivalent to each other. Thus, while a signed zero input most commonly determines the sign of a zero result, because of dividing by zero, +0.0 and -0.0 may not be substituted for each other in general. The sign of a zero input also has a non-substitutable effect on the result of some math library methods.

For ordered comparisons using the built-in comparison operators (<, <=, etc.), NaN values have another anomalous situation: a NaN is neither less than, nor greater than, nor equal to any value, including itself. This means the trichotomy of comparison does not hold.

To provide the appropriate semantics for equals and compareTo methods, those methods cannot simply be wrappers around == or ordered comparison operations. Instead, equals uses representation equivalence, defining NaN arguments to be equal to each other, restoring reflexivity, and defining +0.0 to not be equal to -0.0. For comparisons, compareTo defines a total order where -0.0 is less than +0.0 and where a NaN is equal to itself and considered greater than positive infinity.

The operational semantics of equals and compareTo are expressed in terms of bit-wise converting the floating-point values to integral values.

The natural ordering implemented by compareTo is consistent with equals. That is, two objects are reported as equal by equals if and only if compareTo on those objects returns zero.

The adjusted behaviors defined for equals and compareTo allow instances of wrapper classes to work properly with conventional data structures. For example, defining NaN values to be equals to one another allows NaN to be used as an element of a HashSet or as the key of a HashMap. Similarly, defining compareTo as a total ordering, including +0.0, -0.0, and NaN, allows instances of wrapper classes to be used as elements of a SortedSet or as keys of a SortedMap.

Comparing numerical equality to various useful equivalence relations that can be defined over floating-point values:

numerical equality (== operator): (Not an equivalence relation)
Two floating-point values represent the same extended real number. The extended real numbers are the real numbers augmented with positive infinity and negative infinity. Under numerical equality, +0.0 and -0.0 are equal since they both map to the same real value, 0. A NaN does not map to any real number and is not equal to any value, including itself.
bit-wise equivalence:
The bits of the two floating-point values are the same. This equivalence relation for double values a and b is implemented by the expression
Double.doubleToRawLongBits(a) == Double.doubleToRawLongBits(b)
Under this relation, +0.0 and -0.0 are distinguished from each other and every bit pattern encoding a NaN is distinguished from every other bit pattern encoding a NaN.
representation equivalence:
The two floating-point values represent the same IEEE 754 datum. In particular, for finite values, the sign, exponent, and significand components of the floating-point values are the same. Under this relation:
  • +0.0 and -0.0 are distinguished from each other.
  • every bit pattern encoding a NaN is considered equivalent to each other
  • positive infinity is equivalent to positive infinity; negative infinity is equivalent to negative infinity.
Expressions implementing this equivalence relation include:
  • Double.doubleToLongBits(a) == Double.doubleToLongBits(b)
  • Double.valueOf(a).equals(Double.valueOf(b))
  • Double.compare(a, b) == 0
Note that representation equivalence is often an appropriate notion of equivalence to test the behavior of math libraries.
For two binary floating-point values a and b, if neither of a and b is zero or NaN, then the three relations numerical equality, bit-wise equivalence, and representation equivalence of a and b have the same true/false value. In other words, for binary floating-point values, the three relations only differ if at least one argument is zero or NaN.

Decimal ↔ Binary Conversion Issues

Many surprising results of binary floating-point arithmetic trace back to aspects of decimal to binary conversion and binary to decimal conversion. While integer values can be exactly represented in any base, which fractional values can be exactly represented in a base is a function of the base. For example, in base 10, 1/3 is a repeating fraction (0.33333....); but in base 3, 1/3 is exactly 0.1(3), that is 1 × 3-1. Similarly, in base 10, 1/10 is exactly representable as 0.1 (1 × 10-1), but in base 2, it is a repeating fraction (0.0001100110011...(2)).

Values of the float type have 24 bits of precision and values of the double type have 53 bits of precision. Therefore, since 0.1 is a repeating fraction in base 2 with a four-bit repeat, 0.1f != 0.1d. In more detail, including hexadecimal floating-point literals:

  • The exact numerical value of 0.1f (0x1.99999a0000000p-4f) is 0.100000001490116119384765625.
  • The exact numerical value of 0.1d (0x1.999999999999ap-4d) is 0.1000000000000000055511151231257827021181583404541015625.
These are the closest float and double values, respectively, to the numerical value of 0.1. These results are consistent with a float value having the equivalent of 6 to 9 digits of decimal precision and a double value having the equivalent of 15 to 17 digits of decimal precision. (The equivalent precision varies according to the different relative densities of binary and decimal values at different points along the real number line.)

This representation hazard of decimal fractions is one reason to use caution when storing monetary values as float or double. Alternatives include:

  • using BigDecimal to store decimal fractional values exactly
  • scaling up so the monetary value is an integer — for example, multiplying by 100 if the value is denominated in cents or multiplying by 1000 if the value is denominated in mills — and then storing that scaled value in an integer type

For each finite floating-point value and a given floating-point type, there is a contiguous region of the real number line which maps to that value. Under the default round to nearest rounding policy (JLS 15.4), this contiguous region for a value is typically one ulp (unit in the last place) wide and centered around the exactly representable value. (At exponent boundaries, the region is asymmetrical and larger on the side with the larger exponent.) For example, for 0.1f, the region can be computed as follows:
// Numeric values listed are exact values
oneTenthApproxAsFloat = 0.100000001490116119384765625;
ulpOfoneTenthApproxAsFloat = Math.ulp(0.1f) = 7.450580596923828125E-9;
// Numeric range that is converted to the float closest to 0.1, _excludes_ endpoints
(oneTenthApproxAsFloat - ½ulpOfoneTenthApproxAsFloat, oneTenthApproxAsFloat + ½ulpOfoneTenthApproxAsFloat) =
(0.0999999977648258209228515625, 0.1000000052154064178466796875)

In particular, a correctly rounded decimal to binary conversion of any string representing a number in this range, say by Float.parseFloat(String), will be converted to the same value: 

Float.parseFloat("0.0999999977648258209228515625000001"); // rounds up to oneTenthApproxAsFloat
Float.parseFloat("0.099999998");                          // rounds up to oneTenthApproxAsFloat
Float.parseFloat("0.1");                                  // rounds up to oneTenthApproxAsFloat
Float.parseFloat("0.100000001490116119384765625");        // exact conversion
Float.parseFloat("0.100000005215406417846679687");        // rounds down to oneTenthApproxAsFloat
Float.parseFloat("0.100000005215406417846679687499999");  // rounds down to oneTenthApproxAsFloat

Similarly, an analogous range can be constructed for the double type based on the exact value of double approximation to 0.1d and the numerical value of Math.ulp(0.1d) and likewise for other particular numerical values in the float and double types.

As seen in the above conversions, compared to the exact numerical value the operation would have without rounding, the same floating-point value as a result can be:

  • greater than the exact result
  • equal to the exact result
  • less than the exact result
A floating-point value doesn't "know" whether it was the result of rounding up, or rounding down, or an exact operation; it contains no history of how it was computed. Consequently, the sum of 
0.1f + 0.1f + 0.1f + 0.1f + 0.1f + 0.1f + 0.1f + 0.1f + 0.1f + 0.1f;
// Numerical value of computed sum: 1.00000011920928955078125,
// the next floating-point value larger than 1.0f, equal to Math.nextUp(1.0f).
or 
0.1d + 0.1d + 0.1d + 0.1d + 0.1d + 0.1d + 0.1d + 0.1d + 0.1d + 0.1d;
// Numerical value of computed sum: 0.99999999999999988897769753748434595763683319091796875,
// the next floating-point value smaller than 1.0d, equal to Math.nextDown(1.0d).
should not be expected to be exactly equal to 1.0, but only to be close to 1.0. Consequently, the following code is an infinite loop: 
double d = 0.0;
while (d != 1.0) { // Surprising infinite loop
  d += 0.1; // Sum never _exactly_ equals 1.0
}
Instead, use an integer loop count for counted loops: 
double d = 0.0;
for (int i = 0; i < 10; i++) {
  d += 0.1;
} // Value of d is equal to Math.nextDown(1.0).
or test against a floating-point limit using ordered comparisons (<, <=, >, >=): 
double d = 0.0;
while (d <= 1.0) {
  d += 0.1;
} // Value of d approximately 1.0999999999999999
While floating-point arithmetic may have surprising results, IEEE 754 floating-point arithmetic follows a principled design and its behavior is predictable on the Java platform.
See Java Language Specification:
4.2.3 Floating-Point Types and Values
4.2.4 Floating-Point Operations
15.21.1 Numerical Equality Operators == and !=
15.20.1 Numerical Comparison Operators <, <=, >, and >=
Since:
1.0
See Also:

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final int
    BYTES
    The number of bytes used to represent a double value, 8.
    static final int
    MAX_EXPONENT
    Maximum exponent a finite double variable may have, 1023.
    static final double
    MAX_VALUE
    A constant holding the largest positive finite value of type double, (2-2-52)·21023.
    static final int
    MIN_EXPONENT
    Minimum exponent a normalized double variable may have, -1022.
    static final double
    MIN_NORMAL
    A constant holding the smallest positive normal value of type double, 2-1022.
    static final double
    MIN_VALUE
    A constant holding the smallest positive nonzero value of type double, 2-1074.
    static final double
    NaN
    A constant holding a Not-a-Number (NaN) value of type double.
    static final double
    NEGATIVE_INFINITY
    A constant holding the negative infinity of type double.
    static final double
    POSITIVE_INFINITY
    A constant holding the positive infinity of type double.
    static final int
    PRECISION
    The number of bits in the significand of a double value, 53.
    static final int
    SIZE
    The number of bits used to represent a double value, 64.
    static final Class<Double>
    TYPE
    The Class instance representing the primitive type double.

  • Constructor Summary

    Constructors
    Constructor
    Description
    Double(double value)
    Deprecated, for removal: This API element is subject to removal in a future version.
    It is rarely appropriate to use this constructor.
    Double(String s)
    Deprecated, for removal: This API element is subject to removal in a future version.
    It is rarely appropriate to use this constructor.

  • Method Summary

    Modifier and Type
    Method
    Description
    byte
    byteValue()
    Returns the value of this Double as a byte after a narrowing primitive conversion.
    static int
    compare(double d1, double d2)
    Compares the two specified double values.
    int
    compareTo(Double anotherDouble)
    Compares two Double objects numerically.
    Optional<Double>
    describeConstable()
    Returns an Optional containing the nominal descriptor for this instance, which is the instance itself.
    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 value of this Double as a float after a narrowing primitive conversion.
    int
    hashCode()
    Returns a hash code for this Double object.
    static int
    hashCode(double value)
    Returns a hash code for a double value; compatible with Double.hashCode().
    int
    intValue()
    Returns the value of this Double as an int after a narrowing primitive conversion.
    static boolean
    isFinite(double d)
    Returns true if the argument is a finite floating-point value; returns false otherwise (for NaN and infinity arguments).
    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 after a narrowing primitive conversion.
    static double
    max(double a, double b)
    Returns the greater of two double values as if by calling Math.max.
    static double
    min(double a, double b)
    Returns the smaller of two double values as if by calling Math.min.
    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.
    Double
    resolveConstantDesc(MethodHandles.Lookup lookup)
    Resolves this instance as a ConstantDesc, the result of which is the instance itself.
    short
    shortValue()
    Returns the value of this Double as a short after a narrowing primitive conversion.
    static double
    sum(double a, double b)
    Adds two double values together as per the + operator.
    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 declared in class java.lang.Object

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

  • Field Details

    • 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:

    • 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:

    • 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:

    • 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:

    • 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:

    • 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:

    • SIZE

      public static final int SIZE
      The number of bits used to represent a double value, 64.
      Since:
      1.5
      See Also:

    • PRECISION

      public static final int PRECISION
      The number of bits in the significand of a double value, 53. This is the parameter N in section 4.2.3 of The Java Language Specification.
      Since:
      19
      See Also:

    • MAX_EXPONENT

      public static final int MAX_EXPONENT
      Maximum exponent a finite double variable may have, 1023. It is equal to the value returned by Math.getExponent(Double.MAX_VALUE).
      Since:
      1.6
      See Also:

    • MIN_EXPONENT

      public static final int MIN_EXPONENT
      Minimum exponent a normalized double variable may have, -1022. It is equal to the value returned by Math.getExponent(Double.MIN_NORMAL).
      Since:
      1.6
      See Also:

    • BYTES

      public static final int BYTES
      The number of bytes used to represent a double value, 8.
      Since:
      1.8
      See Also:

    • TYPE

      public static final Class<Double> TYPE
      The Class instance representing the primitive type double.
      Since:
      1.1

  • Constructor Details

    • Double

      @Deprecated(since="9", forRemoval=true) public Double(double value)
      Deprecated, for removal: This API element is subject to removal in a future version.
      It is rarely appropriate to use this constructor. The static factory valueOf(double) is generally a better choice, as it is likely to yield significantly better space and time performance.
      Constructs a newly allocated Double object that represents the primitive double argument.
      Parameters:
      value - the value to be represented by the Double.

    • Double

      @Deprecated(since="9", forRemoval=true) public Double(String s) throws NumberFormatException
      Deprecated, for removal: This API element is subject to removal in a future version.
      It is rarely appropriate to use this constructor. Use parseDouble(String) to convert a string to a double primitive, or use valueOf(String) to convert a string to a Double object.
      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.

  • Method Details

    • 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".
        • Otherwise m is positive and finite. It is converted to a string in two stages:
          • Selection of a decimal: A well-defined decimal dm is selected to represent m. This decimal is (almost always) the shortest one that rounds to m according to the round to nearest rounding policy of IEEE 754 floating-point arithmetic.
          • Formatting as a string: The decimal dm is formatted as a string, either in plain or in computerized scientific notation, depending on its value.

      A decimal is a number of the form s×10i for some (unique) integers s > 0 and i such that s is not a multiple of 10. These integers are the significand and the exponent, respectively, of the decimal. The length of the decimal is the (unique) positive integer n meeting 10n-1 ≤ s < 10n.

      The decimal dm for a finite positive m is defined as follows:

      • Let R be the set of all decimals that round to m according to the usual round to nearest rounding policy of IEEE 754 floating-point arithmetic.
      • Let p be the minimal length over all decimals in R.
      • When p ≥ 2, let T be the set of all decimals in R with length p. Otherwise, let T be the set of all decimals in R with length 1 or 2.
      • Define dm as the decimal in T that is closest to m. Or if there are two such decimals in T, select the one with the even significand.

      The (uniquely) selected decimal dm is then formatted. Let s, i and n be the significand, exponent and length of dm, respectively. Further, let e = n + i - 1 and let s1…sn be the usual decimal expansion of s. Note that s1 ≠ 0 and sn ≠ 0. Below, the decimal point '.' is '\u002E' and the exponent indicator 'E' is '\u0045'.

      • Case -3 ≤ e < 0: dm is formatted as 0.0…0s1…sn, where there are exactly -(n + i) zeroes between the decimal point and s1. For example, 123 × 10-4 is formatted as 0.0123.
      • Case 0 ≤ e < 7:
        • Subcase i ≥ 0: dm is formatted as s1…sn0…0.0, where there are exactly i zeroes between sn and the decimal point. For example, 123 × 102 is formatted as 12300.0.
        • Subcase i < 0: dm is formatted as s1…sn+i.sn+i+1…sn, where there are exactly -i digits to the right of the decimal point. For example, 123 × 10-1 is formatted as 12.3.
      • Case e < -3 or e ≥ 7: computerized scientific notation is used to format dm. Here e is formatted as by Integer.toString(int).
        • Subcase n = 1: dm is formatted as s1.0Ee. For example, 1 × 1023 is formatted as 1.0E23.
        • Subcase n > 1: dm is formatted as s1.s2…snEe. For example, 123 × 10-21 is formatted as 1.23E-19.

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

      API Note:
      This method corresponds to the general functionality of the convertToDecimalCharacter operation defined in IEEE 754; however, that operation is defined in terms of specifying the number of significand digits used in the conversion. Code to do such a conversion in the Java platform includes converting the double to a BigDecimal exactly and then rounding the BigDecimal to the desired number of digits; sample code: 
      double d = 0.1;
int digits = 25;
BigDecimal bd = new BigDecimal(d);
String result = bd.round(new MathContext(digits,  RoundingMode.HALF_UP));
// 0.1000000000000000055511151
      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.
      • If the argument is NaN, the result is the string "NaN".
      • Otherwise, the result is a string that represents the sign and magnitude 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 string "Infinity"; thus, positive infinity produces the result "Infinity" and negative infinity produces the result "-Infinity".
        • If m is zero, it is represented by the string "0x0.0p0"; thus, negative zero produces the result "-0x0.0p0" and positive zero produces the result "0x0.0p0".
        • If m is a double value with a normalized representation, substrings are used to represent the significand and exponent fields. The significand is represented by the characters "0x1." followed by a lowercase hexadecimal representation of the rest of the significand as a fraction. Trailing zeros in the hexadecimal representation are removed unless all the digits are zero, in which case a single zero is used. Next, the exponent is represented by "p" followed by a decimal string of the unbiased exponent as if produced by a call to Integer.toString on the exponent value.
        • If m is a double value with a subnormal representation, the significand is represented by the characters "0x0." followed by a hexadecimal representation of the rest of the significand as a fraction. Trailing zeros in the hexadecimal representation are removed. Next, the exponent is represented by "p-1022". Note that there must be at least one nonzero digit in a subnormal significand.
      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
      API Note:
      This method corresponds to the convertToHexCharacter operation defined in IEEE 754.
      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 Java Language Specification, except that underscores are not accepted between digits. 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. Note that the round-to-nearest rule also implies overflow and underflow behaviour; if the exact value of s is large enough in magnitude (greater than or equal to (MAX_VALUE + ulp(MAX_VALUE)/2), rounding to double will result in an infinity and if the exact value of s is small enough in magnitude (less than or equal to MIN_VALUE/2), rounding to float will result in a zero. Finally, after rounding a Double object representing this double value is returned.

      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 section 3.10.2 of
      // The Java Language Specification.

      // 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
 }
      API Note:
      To interpret localized string representations of a floating-point value, or string representations that have non-ASCII digits, use NumberFormat. For example, 
          NumberFormat.getInstance(l).parse(s).doubleValue();
      where l is the desired locale, or Locale.ROOT if locale insensitive., This method corresponds to the convertFromDecimalCharacter and convertFromHexCharacter operations defined in IEEE 754.
      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.
      See Also:

    • 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:
      NullPointerException - if the string is null
      NumberFormatException - if the string does not contain a parsable double.
      Since:
      1.2
      See Also:

    • isNaN

      public static boolean isNaN(double v)
      Returns true if the specified number is a Not-a-Number (NaN) value, false otherwise.
      API Note:
      This method corresponds to the isNaN operation defined in IEEE 754.
      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.
      API Note:
      This method corresponds to the isInfinite operation defined in IEEE 754.
      Parameters:
      v - the value to be tested.
      Returns:
      true if the value of the argument is positive infinity or negative infinity; false otherwise.

    • isFinite

      public static boolean isFinite(double d)
      Returns true if the argument is a finite floating-point value; returns false otherwise (for NaN and infinity arguments).
      API Note:
      This method corresponds to the isFinite operation defined in IEEE 754.
      Parameters:
      d - the double value to be tested
      Returns:
      true if the argument is a finite floating-point value, false otherwise.
      Since:
      1.8

    • 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:

    • byteValue

      public byte byteValue()
      Returns the value of this Double as a byte after a narrowing primitive conversion.
      Overrides:
      byteValue in class Number
      Returns:
      the double value represented by this object converted to type byte
      See Java Language Specification:
      5.1.3 Narrowing Primitive Conversion
      Since:
      1.1

    • shortValue

      public short shortValue()
      Returns the value of this Double as a short after a narrowing primitive conversion.
      Overrides:
      shortValue in class Number
      Returns:
      the double value represented by this object converted to type short
      See Java Language Specification:
      5.1.3 Narrowing Primitive Conversion
      Since:
      1.1

    • intValue

      public int intValue()
      Returns the value of this Double as an int after a narrowing primitive conversion.
      Specified by:
      intValue in class Number
      API Note:
      This method corresponds to the convertToIntegerTowardZero operation defined in IEEE 754.
      Returns:
      the double value represented by this object converted to type int
      See Java Language Specification:
      5.1.3 Narrowing Primitive Conversion

    • longValue

      public long longValue()
      Returns the value of this Double as a long after a narrowing primitive conversion.
      Specified by:
      longValue in class Number
      API Note:
      This method corresponds to the convertToIntegerTowardZero operation defined in IEEE 754.
      Returns:
      the double value represented by this object converted to type long
      See Java Language Specification:
      5.1.3 Narrowing Primitive Conversion

    • floatValue

      public float floatValue()
      Returns the value of this Double as a float after a narrowing primitive conversion.
      Specified by:
      floatValue in class Number
      API Note:
      This method corresponds to the convertFormat operation defined in IEEE 754.
      Returns:
      the double value represented by this object converted to type float
      See Java Language Specification:
      5.1.3 Narrowing Primitive Conversion
      Since:
      1.0

    • 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:

    • hashCode

      public static int hashCode(double value)
      Returns a hash code for a double value; compatible with Double.hashCode().
      Parameters:
      value - the value to hash
      Returns:
      a hash code value for a double value.
      Since:
      1.8

    • 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.
      Overrides:
      equals in class Object
      API Note:
      This method is defined in terms of doubleToLongBits(double) rather than the == operator on double values since the == operator does not define an equivalence relation and to satisfy the equals contract an equivalence relation must be implemented; see this discussion for details of floating-point equality and equivalence.
      Parameters:
      obj - the reference object with which to compare.
      Returns:
      true if this object is the same as the obj argument; false otherwise.
      See Java Language Specification:
      15.21.1 Numerical Equality Operators == and !=
      See Also:

    • 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. This method imposes a total order on Double objects with two differences compared to the incomplete order defined by the Java language numerical comparison operators (<, <=, ==, >=, >) on double values.
      • A NaN is unordered with respect to other values and unequal to itself under the comparison operators. This method chooses to define Double.NaN to be equal to itself and greater than all other double values (including Double.POSITIVE_INFINITY).
      • Positive zero and negative zero compare equal numerically, but are distinct and distinguishable values. This method chooses to define positive zero (+0.0d), to be greater than negative zero (-0.0d).
      This ensures that the natural ordering of Double objects imposed by this method is consistent with equals; see this discussion for details of floating-point comparison and ordering.
      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.
      See Java Language Specification:
      15.20.1 Numerical Comparison Operators <, <=, >, and >=
      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: 
          Double.valueOf(d1).compareTo(Double.valueOf(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

    • sum

      public static double sum(double a, double b)
      Adds two double values together as per the + operator.
      API Note:
      This method corresponds to the addition operation defined in IEEE 754.
      Parameters:
      a - the first operand
      b - the second operand
      Returns:
      the sum of a and b
      See Java Language Specification:
      4.2.4 Floating-Point Operations
      Since:
      1.8
      See Also:

    • max

      public static double max(double a, double b)
      Returns the greater of two double values as if by calling Math.max.
      API Note:
      This method corresponds to the maximum operation defined in IEEE 754.
      Parameters:
      a - the first operand
      b - the second operand
      Returns:
      the greater of a and b
      Since:
      1.8
      See Also:

    • min

      public static double min(double a, double b)
      Returns the smaller of two double values as if by calling Math.min.
      API Note:
      This method corresponds to the minimum operation defined in IEEE 754.
      Parameters:
      a - the first operand
      b - the second operand
      Returns:
      the smaller of a and b.
      Since:
      1.8
      See Also:

    • describeConstable

      public Optional<Double> describeConstable()
      Returns an Optional containing the nominal descriptor for this instance, which is the instance itself.
      Specified by:
      describeConstable in interface Constable
      Returns:
      an Optional describing the Double instance
      Since:
      12

    • resolveConstantDesc

      public Double resolveConstantDesc(MethodHandles.Lookup lookup)
      Resolves this instance as a ConstantDesc, the result of which is the instance itself.
      Specified by:
      resolveConstantDesc in interface ConstantDesc
      Parameters:
      lookup - ignored
      Returns:
      the Double instance
      Since:
      12