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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 System.DateTime structure.

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 long.

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 long datetime from the given time scale to the universal time scale.

static BigDecimal bigDecimalFrom(double otherTime, int timeScale)

Convert a double datetime from the given time scale to the universal time scale.

static BigDecimal bigDecimalFrom(BigDecimal otherTime, int timeScale)

Convert a BigDecimal datetime from the given time scale to the universal time scale.

static long from(long otherTime, int timeScale)

Convert a long datetime from the given time scale to the universal time scale.

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 BigDecimal in the given time scale.

static BigDecimal toBigDecimal(BigDecimal universalTime, int timeScale)

Convert a datetime from the universal time scale to a BigDecimal in the given time scale.

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.

Inherited methods

Constants

DB2_TIME

added in API level 26
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

added in API level 26
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

added in API level 26
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.

Constant Value: 6 (0x00000006)

EPOCH_OFFSET_VALUE

added in API level 26
public static final int EPOCH_OFFSET_VALUE

The constant used to select the epoch offset value for a time scale.

Constant Value: 1 (0x00000001)

EXCEL_TIME

added in API level 26
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

added in API level 26
public static final int FROM_MAX_VALUE

The constant used to select the maximum from value for a time scale.

Constant Value: 3 (0x00000003)

FROM_MIN_VALUE

added in API level 26
public static final int FROM_MIN_VALUE

The constant used to select the minimum from value for a time scale.

Constant Value: 2 (0x00000002)

ICU4C_TIME

added in API level 26
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

added in API level 26
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

added in API level 26
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

added in API level 26
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

added in API level 26
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

added in API level 26
public static final int TO_MAX_VALUE

The constant used to select the maximum to value for a time scale.

Constant Value: 5 (0x00000005)

TO_MIN_VALUE

added in API level 26
public static final int TO_MIN_VALUE

The constant used to select the minimum to value for a time scale.

Constant Value: 4 (0x00000004)

UNITS_VALUE

added in API level 26
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

added in API level 26
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

added in API level 26
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

added in API level 26
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

added in API level 26
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

added in API level 26
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

added in API level 26
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

added in API level 26
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

added in API level 26
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

added in API level 26
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

added in API level 26
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

added in API level 26
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