UniversalTimeScale
public
final
class
UniversalTimeScale
extends Object
java.lang.Object | |
↳ | android.icu.util.UniversalTimeScale |
There are quite a few different conventions for binary datetime, depending on different
platforms and protocols. Some of these have severe drawbacks. For example, people using
Unix time (seconds since Jan 1, 1970, usually in a 32-bit integer)
think that they are safe until near the year 2038.
But cases can and do arise where arithmetic manipulations causes serious problems. Consider
the computation of the average of two datetimes, for example: if one calculates them with
averageTime = (time1 + time2)/2
, there will be overflow even with dates
beginning in 2004. Moreover, even if these problems don't occur, there is the issue of
conversion back and forth between different systems.
Binary datetimes differ in a number of ways: the datatype, the unit, and the epoch (origin). We refer to these as time scales.
ICU implements a universal time scale that is similar to the .NET framework's System.DateTime. The universal time scale is a 64-bit integer that holds ticks since midnight, January 1st, 0001. (One tick is 100 nanoseconds.) Negative values are supported. This has enough range to guarantee that calculations involving dates around the present are safe.
The universal time scale always measures time according to the proleptic Gregorian calendar. That is, the Gregorian calendar's leap year rules are used for all times, even before 1582 when it was introduced. (This is different from the default ICU calendar which switches from the Julian to the Gregorian calendar in 1582. See GregorianCalendar.setGregorianChange() and ucal_setGregorianChange().) ICU provides conversion functions to and from all other major time scales, allowing datetimes in any time scale to be converted to the universal time scale, safely manipulated, and converted back to any other datetime time scale.
For more details and background, see the Universal Time Scale chapter in the ICU User Guide.
Summary
Constants | |
---|---|
int |
DB2_TIME
Used in DB2. |
int |
DOTNET_DATE_TIME
Used in the .NET framework's |
int |
EPOCH_OFFSET_PLUS_1_VALUE
The constant used to select the epoch plus one value for a time scale. |
int |
EPOCH_OFFSET_VALUE
The constant used to select the epoch offset value for a time scale. |
int |
EXCEL_TIME
Used in Excel. |
int |
FROM_MAX_VALUE
The constant used to select the maximum from value for a time scale. |
int |
FROM_MIN_VALUE
The constant used to select the minimum from value for a time scale. |
int |
ICU4C_TIME
Used in the ICU4C. |
int |
JAVA_TIME
Used in the JDK. |
int |
MAC_OLD_TIME
Used in older Macintosh systems. |
int |
MAC_TIME
Used in the JDK. |
int |
MAX_SCALE
This constant was deprecated in API level 28. ICU 59 |
int |
TO_MAX_VALUE
The constant used to select the maximum to value for a time scale. |
int |
TO_MIN_VALUE
The constant used to select the minimum to value for a time scale. |
int |
UNITS_VALUE
The constant used to select the units value for a time scale. |
int |
UNIX_MICROSECONDS_TIME
Data is a |
int |
UNIX_TIME
Used in Unix systems. |
int |
WINDOWS_FILE_TIME
Used in Windows for file times. |
Public methods | |
---|---|
static
BigDecimal
|
bigDecimalFrom(long otherTime, int timeScale)
Convert a |
static
BigDecimal
|
bigDecimalFrom(double otherTime, int timeScale)
Convert a |
static
BigDecimal
|
bigDecimalFrom(BigDecimal otherTime, int timeScale)
Convert a |
static
long
|
from(long otherTime, int timeScale)
Convert a |
static
long
|
getTimeScaleValue(int scale, int value)
Get a value associated with a particular time scale. |
static
BigDecimal
|
toBigDecimal(long universalTime, int timeScale)
Convert a datetime from the universal time scale to a |
static
BigDecimal
|
toBigDecimal(BigDecimal universalTime, int timeScale)
Convert a datetime from the universal time scale to a |
static
long
|
toLong(long universalTime, int timeScale)
Convert a datetime from the universal time scale stored as a |
Inherited methods | |
---|---|
Constants
DB2_TIME
public static final int DB2_TIME
Used in DB2. Data is a ?unknown?
. Value
is days since December 31, 1899.
Constant Value: 8 (0x00000008)
DOTNET_DATE_TIME
public static final int DOTNET_DATE_TIME
Used in the .NET framework's System.DateTime
structure.
Data is a long
. Value is ticks (1 tick == 100 nanoseconds) since January 1, 0001.
Constant Value: 4 (0x00000004)
EPOCH_OFFSET_PLUS_1_VALUE
public static final int EPOCH_OFFSET_PLUS_1_VALUE
The constant used to select the epoch plus one value for a time scale. NOTE: This is an internal value. DO NOT USE IT. May not actually be equal to the epoch offset value plus one.
See also:
Constant Value: 6 (0x00000006)
EPOCH_OFFSET_VALUE
public static final int EPOCH_OFFSET_VALUE
The constant used to select the epoch offset value for a time scale.
See also:
Constant Value: 1 (0x00000001)
EXCEL_TIME
public static final int EXCEL_TIME
Used in Excel. Data is a ?unknown?
. Value
is days since December 31, 1899.
Constant Value: 7 (0x00000007)
FROM_MAX_VALUE
public static final int FROM_MAX_VALUE
The constant used to select the maximum from value for a time scale.
See also:
Constant Value: 3 (0x00000003)
FROM_MIN_VALUE
public static final int FROM_MIN_VALUE
The constant used to select the minimum from value for a time scale.
See also:
Constant Value: 2 (0x00000002)
ICU4C_TIME
public static final int ICU4C_TIME
Used in the ICU4C. Data is a double
. Value
is milliseconds since January 1, 1970.
Constant Value: 2 (0x00000002)
JAVA_TIME
public static final int JAVA_TIME
Used in the JDK. Data is a long
. Value
is milliseconds since January 1, 1970.
Constant Value: 0 (0x00000000)
MAC_OLD_TIME
public static final int MAC_OLD_TIME
Used in older Macintosh systems. Data is an int
. Value
is seconds since January 1, 1904.
Constant Value: 5 (0x00000005)
MAC_TIME
public static final int MAC_TIME
Used in the JDK. Data is a double
. Value
is milliseconds since January 1, 2001.
Constant Value: 6 (0x00000006)
MAX_SCALE
public static final int MAX_SCALE
This constant was deprecated
in API level 28.
ICU 59
This is the first unused time scale value.
Constant Value: 10 (0x0000000a)
TO_MAX_VALUE
public static final int TO_MAX_VALUE
The constant used to select the maximum to value for a time scale.
See also:
Constant Value: 5 (0x00000005)
TO_MIN_VALUE
public static final int TO_MIN_VALUE
The constant used to select the minimum to value for a time scale.
See also:
Constant Value: 4 (0x00000004)
UNITS_VALUE
public static final int UNITS_VALUE
The constant used to select the units value for a time scale.
Constant Value: 0 (0x00000000)
UNIX_MICROSECONDS_TIME
public static final int UNIX_MICROSECONDS_TIME
Data is a long
. Value is microseconds since January 1, 1970.
Similar to Unix time (linear value from 1970) and struct timeval
(microseconds resolution).
Constant Value: 9 (0x00000009)
UNIX_TIME
public static final int UNIX_TIME
Used in Unix systems. Data is an int
or a long
. Value
is seconds since January 1, 1970.
Constant Value: 1 (0x00000001)
WINDOWS_FILE_TIME
public static final int WINDOWS_FILE_TIME
Used in Windows for file times. Data is a long
. Value
is ticks (1 tick == 100 nanoseconds) since January 1, 1601.
Constant Value: 3 (0x00000003)
Public methods
bigDecimalFrom
public static BigDecimal bigDecimalFrom (long otherTime, int timeScale)
Convert a long
datetime from the given time scale to the universal time scale.
All calculations are done using BigDecimal
to guarantee that the value
does not go out of range.
Parameters | |
---|---|
otherTime |
long : The long datetime |
timeScale |
int : The time scale to convert from |
Returns | |
---|---|
BigDecimal |
The datetime converted to the universal time scale |
bigDecimalFrom
public static BigDecimal bigDecimalFrom (double otherTime, int timeScale)
Convert a double
datetime from the given time scale to the universal time scale.
All calculations are done using BigDecimal
to guarantee that the value
does not go out of range.
Parameters | |
---|---|
otherTime |
double : The double datetime |
timeScale |
int : The time scale to convert from |
Returns | |
---|---|
BigDecimal |
The datetime converted to the universal time scale |
bigDecimalFrom
public static BigDecimal bigDecimalFrom (BigDecimal otherTime, int timeScale)
Convert a BigDecimal
datetime from the given time scale to the universal time scale.
All calculations are done using BigDecimal
to guarantee that the value
does not go out of range.
Parameters | |
---|---|
otherTime |
BigDecimal : The BigDecimal datetime |
timeScale |
int : The time scale to convert from |
Returns | |
---|---|
BigDecimal |
The datetime converted to the universal time scale |
from
public static long from (long otherTime, int timeScale)
Convert a long
datetime from the given time scale to the universal time scale.
Parameters | |
---|---|
otherTime |
long : The long datetime |
timeScale |
int : The time scale to convert from |
Returns | |
---|---|
long |
The datetime converted to the universal time scale |
getTimeScaleValue
public static long getTimeScaleValue (int scale, int value)
Get a value associated with a particular time scale.
Parameters | |
---|---|
scale |
int : - the time scale |
value |
int : - a constant representing the value to get |
Returns | |
---|---|
long |
- the value. |
toBigDecimal
public static BigDecimal toBigDecimal (long universalTime, int timeScale)
Convert a datetime from the universal time scale to a BigDecimal
in the given time scale.
Parameters | |
---|---|
universalTime |
long : The datetime in the universal time scale |
timeScale |
int : The time scale to convert to |
Returns | |
---|---|
BigDecimal |
The datetime converted to the given time scale |
toBigDecimal
public static BigDecimal toBigDecimal (BigDecimal universalTime, int timeScale)
Convert a datetime from the universal time scale to a BigDecimal
in the given time scale.
Parameters | |
---|---|
universalTime |
BigDecimal : The datetime in the universal time scale |
timeScale |
int : The time scale to convert to |
Returns | |
---|---|
BigDecimal |
The datetime converted to the given time scale |
toLong
public static long toLong (long universalTime, int timeScale)
Convert a datetime from the universal time scale stored as a BigDecimal
to a
long
in the given time scale.
Since this calculation requires a divide, we must round. The straight forward
way to round by adding half of the divisor will push the sum out of range for values
within have the divisor of the limits of the precision of a long
. To get around this, we do
the rounding like this:
(universalTime - units + units/2) / units + 1
(i.e. we subtract units first to guarantee that we'll still be in range when we
add units/2
. We then need to add one to the quotent to make up for the extra subtraction.
This simplifies to:
(universalTime - units/2) / units - 1
For negative values to round away from zero, we need to flip the signs:
(universalTime + units/2) / units + 1
Since we also need to subtract the epochOffset, we fold the +/- 1
into the offset value. (i.e. epochOffsetP1
, epochOffsetM1
.)
Parameters | |
---|---|
universalTime |
long : The datetime in the universal time scale |
timeScale |
int : The time scale to convert to |
Returns | |
---|---|
long |
The datetime converted to the given time scale |