
Chapter 10 The java.lang Package 

Double
Name
Double
 Class Name:

java.lang.Double
 Superclass:

java.lang.Number
 Immediate Subclasses:

None
 Interfaces Implemented:

None
 Availability:

JDK 1.0 or later
The Double class provides an object wrapper
for a double value. This is useful when you need
to treat a double value as an object. For example,
there are a number of utility methods that take a reference to an
Object as one of their arguments. You cannot
specify a double value for one of these arguments,
but you can provide a reference to a Double object
that encapsulates the double value. Furthermore,
as of JDK 1.1, the Double class is necessary to
support the Reflection API and class literals.
In Java, double values are represented
using the IEEE 754 format. The Double class provides
constants for the three special values that are mandated by this format:
POSITIVE_INFINITY, NEGATIVE_INFINITY,
and NaN (notanumber).
The Double class also provides some utility
methods, such as methods for determining whether a double
value is an infinity value or NaN, for converting double
values to other primitive types, and for converting a double
to a String and vice versa.
public final class java.lang.Double extends java.lang.Number {
// Constants
public final static double MAX_VALUE;
public final static double MIN_VALUE;
public final static double NaN;
public final static double NEGATIVE_INFINITY;
public final static double POSITIVE_INFINITY;
public final static Class TYPE; // New in 1.1
// Constructors
public Double(double value);
public Double(String s);
// Class Methods
public static native long doubleToLongBits(double value);
public static boolean isInfinite(double v);
public static boolean isNaN(double v);
public static native double longBitsToDouble(long bits);
public static String toString(double d);
public static Double valueOf(String s);
// Instance Methods
public byte byteValue(); // New in 1.1
public double doubleValue();
public boolean equals(Object obj);
public float floatValue();
public int hashCode();
public int intValue();
public boolean isInfinite();
public boolean isNaN();
public long longValue();
public short shortValue(); // New in 1.1
public String toString();
}
 Description

The largest value that can be represented by a double.
 Description

The smallest value that can be represented by a double.
 Description

This variable represents the value notanumber (NaN), which is a
special value produced by double operations such as
division of zero by zero. When NaN is one of the operands, most
arithmetic operations return NaN as the result.
Most comparison operators (<,
<=, ==,
>=, >) return
false when one of their arguments is NaN. The
exception is !=, which returns
true when one of its arguments is NaN.
 Description

This variable represents the value negative infinity, which
is produced when a double operation underflows
or a negative double value is divided by zero.
Negative infinity is by definition less than any other double
value.
 Description

This variable represents the value positive infinity, which
is produced when a double operation overflows
or a positive double value is divided by zero.
Positive infinity is by definition greater than any other double
value.
 Availability

New as of JDK 1.1
 Description

The Class object that represents the type
double.
It is always true that Double.TYPE
== double.class.
 Parameters

 value

The double value to be encapsulated
by this object.
 Description

Creates a Double object with the specified
double value.
 Parameters

 s

The string to be made into a Double
object.
 Throws

 NumberFormatException

If the sequence of characters in the given String
does not form a valid double literal.
 Description

Constructs a Double object with the value
specified by the given string. The string must contain a sequence
of characters that forms a legal double literal.
 Parameters

 value

The double value to be converted.
 Returns

The long value that contains the same sequence
of bits as the representation of the given double value.
 Description

This method returns the long value that
contains the same sequence of bits as the representation of the
given double value. The meaning of the bits in
the result is defined by the IEEE 754 floatingpoint format: bit
63 is the sign bit, bits 6252 are the exponent, and bits 510 are
the mantissa.
An argument of POSITIVE_INFINITY
produces the result 0x7ff0000000000000L, an argument
of NEGATIVE_INFINITY produces the result 0xfff0000000000000L,
and an argument of NaN produces the result 0x7ff8000000000000L.
The value returned by this method can be converted back to
the original double value by the longBitsToDouble() method.
 Parameters

 v

The double value to be tested.
 Returns

true if the specified value is equal to
POSITIVE_INFINITY or NEGATIVE_INFINITY;
otherwise false.
 Description

This method determines whether or not the specified value
is an infinity value.
 Parameters

 v

The double value to be tested.
 Returns

true if the specified value is equal to
NaN; otherwise false.
 Description

This method determines whether or not the specified value
is NaN.
 Parameters

 bits

The long value to be converted.
 Returns

The double value whose representation is
the same as the bits in the given long value.
 Description

This method returns the double value whose
representation is the same as the bits in the given double
value. The meaning of the bits in the long
value is defined by the IEEE 754 floatingpoint format: bit 63 is
the sign bit, bits 6252 are the exponent, and bits 510 are the
mantissa. The argument 0x7f80000000000000L produces
the result POSITIVE_INFINITY and the argument
0xff80000000000000L produces the result NEGATIVE_INFINITY.
Arguments in the ranges 0x7ff0000000000001L through
0x7fffffffffffffffL and 0xfff0000000000001L
through 0xffffffffffffffffL all produce the result
NaN.
Except for NaN values not normally used by Java, this method
is the inverse of the doubleToLongBits() method.
 Parameters

 d

The double value to be converted.
 Returns

A string representation of the given value.
 Description

This method returns a String object that
contains a representation of the given double value.
The values NaN, NEGATIVE_INFINITY,
POSITIVE_INFINITY, 0.0, and
+0.0 are represented by
the strings "NaN", "Infinity",
"Infinity", "0.0",
and "0.0", respectively.
For other values, the exact string representation depends
on the value being converted. If the absolute value of d
is greater than or equal to 10^3
or less than or equal to 10^7, it
is converted to a string with an optional minus sign (if the
value is negative) followed by up to eight digits
before the decimal point, a decimal point, and the necessary number
of digits after the decimal point (but no trailing zero if there is
more than one significant digit). There is always a minimum of
one digit after the decimal point.
Otherwise, the value is converted to a string with an optional
minus sign (if the value is negative), followed by a single digit,
a decimal point, the necessary number of digits after the decimal
point (but no trailing zero if there is more than one significant digit),
and the letter E followed by a plus or a minus
sign and a base 10 exponent of at least one digit. Again, there is always
a minimum of one digit after the decimal point.
Note that the definition of this method has changed as of JDK 1.1.
Prior to that release, the method provided a string representation
that was equivalent to the %g format of
the printf function in C.
 Parameters

 s

The string to be made into a Double
object.
 Returns

The Double object constructed from the
string.
 Throws

 NumberFormatException

If the sequence of characters in the given String
does not form a valid double literal.
 Description

Constructs a Double object with the value
specified by the given string. The string must contain a sequence
of characters that forms a legal double literal.
This method ignores leading and trailing white space in the string.
 Availability

New as of JDK 1.1
 Returns

The value of this object as a byte.
 Overrides

Number.byteValue()
 Description

This method returns the truncated value of this object as a
byte. More specifically, if the value of the object
is NaN, the method returns 0. If the value is
POSITIVE_INFINITY, or any other value that is too
large to be represented by an byte, the method
returns Byte.MAX_VALUE. If the value is
NEGATIVE_INFINITY, or any other value that is too
small to be represented by an byte, the method
returns Byte.MIN_VALUE. Otherwise, the value is
rounded toward zero and returned.
 Returns

The value of this object as a double.
 Overrides

Number.doubleValue()
 Description

This method returns the value of this object as a double.
 Parameters

 obj

The object to be compared with this object.
 Returns

true if the objects are equal; false
if they are not.
 Overrides

Object.equals()
 Description

This method returns true if obj
is an instance of Double and it contains the same
value as the object this method is associated with. More specifically,
the method returns true if the
doubleToLongBits() method returns the same result
for the values of both objects.
This method produces a different result than the ==
operator when both values are NaN. In this case,
the == operator produces false,
while this method returns true. By the same token,
the method also produces a different result when the two values
are +0.0 and 0.0. In this
case, the == operator produces true,
while this method returns false.
 Returns

The value of this object as a float.
 Overrides

Number.floatValue()
 Description

This method returns this object value as a float.
Rounding may occur.
 Returns

A hashcode based on the double value of
the object.
 Overrides

Object.hashCode()
 Description

This method returns a hashcode computed from the value of
this object. More specifically, if d is the value
of the object, and bitValue is defined as:
long bitValue = Double.doubleToLongBits(d)
then the hashcode returned by this method is computed as
follows:
(int)(bitValue ^ (bitValue>>>32))
 Returns

The value of this object as an int.
 Overrides

Number.intValue()
 Description

This method returns the truncated value of this object as an
int. More specifically, if the value of the object
is NaN, the method returns 0. If the value is
POSITIVE_INFINITY, or any other value that is too
large to be represented by an int, the method
returns Integer.MAX_VALUE. If the value is
NEGATIVE_INFINITY, or any other value that is too
small to be represented by an int, the method
returns Integer.MIN_VALUE. Otherwise, the value is
rounded toward zero and returned.
 Returns

true if the value of this object is equal
to POSITIVE_INFINITY or NEGATIVE_INFINITY;
otherwise false.
 Description

This method determines whether or not the value of this object
is an infinity value.
 Returns

true if the value of this object is equal
to NaN; otherwise false.
 Description

This method determines whether or not the value of this object
is NaN.
 Returns

The value of this object as a long.
 Overrides

Number.longValue()
 Description

This method returns the truncated value of this object as
a long. More specifically, if the value of the
object is NaN, the method returns 0. If the value
is POSITIVE_INFINITY, or any other value too
large to be represented by a long, the method
returns Long.MAX_VALUE. If the
value is NEGATIVE_INFINITY,
or any other value too small to be represented by a long,
the method returns Long.MIN_VALUE. Otherwise,
the value is rounded toward zero and returned.
 Availability

New as of JDK 1.1
 Returns

The value of this object as a short.
 Overrides

Number.shortValue()
 Description

This method returns the truncated value of this object as a
short. More specifically, if the value of the object
is NaN, the method returns 0. If the value is
POSITIVE_INFINITY, or any other value that is too
large to be represented by an short, the method
returns Short.MAX_VALUE. If the value is
NEGATIVE_INFINITY, or any other value that is too
small to be represented by an short, the method
returns Short.MIN_VALUE. Otherwise, the value is
rounded toward zero and returned.
 Returns

A string representation of the value of this object.
 Overrides

Object.toString()
 Description

This method returns a String object that
contains a representation of the value of this object.
The values NaN, NEGATIVE_INFINITY,
POSITIVE_INFINITY, 0.0, and
+0.0 are represented by
the strings "NaN", "Infinity",
"Infinity", "0.0",
and "0.0", respectively.
For other values, the exact string representation depends
on the value being converted. If the absolute value of this object
is greater than or equal to 10^3
or less than or equal to 10^7, it
is converted to a string with an optional minus sign (if the
value is negative) followed by up to eight digits
before the decimal point, a decimal point, and the necessary number
of digits after the decimal point (but no trailing zero if there is
more than one significant digit). There is always a minimum of
one digit after the decimal point.
Otherwise, the value is converted to a string with an optional
minus sign (if the value is negative), followed by a single digit,
a decimal point, the necessary number of digits after the decimal
point (but no trailing zero if there is more than one significant digit),
and the letter E followed by a plus or a minus
sign and a base 10 exponent of at least one digit. Again, there is always
a minimum of one digit after the decimal point.
Note that the definition of this method has changed as of JDK 1.1.
Prior to that release, the method provided a string representation
that was equivalent to the %g format of
the printf function in C.
