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 32bit 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 64bit 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 P. 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
int DB2_TIME
Used in DB2. Data is a ?unknown?
. Value
is days since December 31, 1899.
Constant Value: 8 (0x00000008)
DOTNET_DATE_TIME
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
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
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
int EXCEL_TIME
Used in Excel. Data is a ?unknown?
. Value
is days since December 31, 1899.
Constant Value: 7 (0x00000007)
FROM_MAX_VALUE
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
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
int ICU4C_TIME
Used in the ICU4C. Data is a double
. Value
is milliseconds since January 1, 1970.
Constant Value: 2 (0x00000002)
JAVA_TIME
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
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
int MAC_TIME
Used in the JDK. Data is a double
. Value
is milliseconds since January 1, 2001.
Constant Value: 6 (0x00000006)
MAX_SCALE
int MAX_SCALE
This constant was deprecated
in API level P.
ICU 59
This is the first unused time scale value.
Constant Value: 10 (0x0000000a)
TO_MAX_VALUE
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
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
int UNITS_VALUE
The constant used to select the units value for a time scale.
Constant Value: 0 (0x00000000)
UNIX_MICROSECONDS_TIME
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
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
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
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
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
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
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
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
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
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
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 