com.ibm.icu.util

Class UniversalTimeScale

java.lang.Object

com.ibm.icu.util.UniversalTimeScale

public final class UniversalTimeScale
extends Object

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.

Field Summary

Fields

Modifier and Type	Field and Description
static int	DB2_TIME Used in DB2.
static int	DOTNET_DATE_TIME Used in the .NET framework's System.DateTime structure.
static int	EPOCH_OFFSET_MINUS_1_VALUE Deprecated. This API is ICU internal only.
static int	EPOCH_OFFSET_PLUS_1_VALUE The constant used to select the epoch plus one value for a time scale.
static int	EPOCH_OFFSET_VALUE The constant used to select the epoch offset value for a time scale.
static int	EXCEL_TIME Used in Excel.
static int	FROM_MAX_VALUE The constant used to select the maximum from value for a time scale.
static int	FROM_MIN_VALUE The constant used to select the minimum from value for a time scale.
static int	ICU4C_TIME Used in the ICU4C.
static int	JAVA_TIME Used in the JDK.
static int	MAC_OLD_TIME Used in older Macintosh systems.
static int	MAC_TIME Used in the JDK.
static int	MAX_ROUND_VALUE Deprecated. This API is ICU internal only.
static int	MAX_SCALE This is the first unused time scale value.
static int	MAX_SCALE_VALUE Deprecated. This API is ICU internal only.
static int	MIN_ROUND_VALUE Deprecated. This API is ICU internal only.
static int	TO_MAX_VALUE The constant used to select the maximum to value for a time scale.
static int	TO_MIN_VALUE The constant used to select the minimum to value for a time scale.
static int	UNITS_ROUND_VALUE Deprecated. This API is ICU internal only.
static int	UNITS_VALUE The constant used to select the units value for a time scale.
static int	UNIX_MICROSECONDS_TIME Data is a long.
static int	UNIX_TIME Used in Unix systems.
static int	WINDOWS_FILE_TIME Used in Windows for file times.

Method Summary

Modifier and Type	Method and Description
static BigDecimal	bigDecimalFrom(BigDecimal otherTime, int timeScale) Convert a BigDecimal 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(long otherTime, int timeScale) Convert a long 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(BigDecimal universalTime, int timeScale) Convert a datetime from the universal time scale to a BigDecimal in the given 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	toBigDecimalTrunc(BigDecimal universalTime, int timeScale) Deprecated. This API is ICU internal only.
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.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

JAVA_TIME

public static final int JAVA_TIME

Used in the JDK. Data is a long. Value is milliseconds since January 1, 1970.

See Also:

Constant Field Values

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.

See Also:

Constant Field Values

ICU4C_TIME

public static final int ICU4C_TIME

Used in the ICU4C. Data is a double. Value is milliseconds since January 1, 1970.

See Also:

Constant Field Values

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.

See Also:

Constant Field Values

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.

See Also:

Constant Field Values

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.

See Also:

Constant Field Values

MAC_TIME

public static final int MAC_TIME

Used in the JDK. Data is a double. Value is milliseconds since January 1, 2001.

See Also:

Constant Field Values

EXCEL_TIME

public static final int EXCEL_TIME

Used in Excel. Data is a ?unknown?. Value is days since December 31, 1899.

See Also:

Constant Field Values

DB2_TIME

public static final int DB2_TIME

Used in DB2. Data is a ?unknown?. Value is days since December 31, 1899.

See Also:

Constant Field Values

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).

See Also:

Constant Field Values

MAX_SCALE

public static final int MAX_SCALE

This is the first unused time scale value.

See Also:

Constant Field Values

UNITS_VALUE

public static final int UNITS_VALUE

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

See Also:

Constant Field Values

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:

getTimeScaleValue(int, int), Constant Field Values

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:

getTimeScaleValue(int, int), Constant Field Values

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:

getTimeScaleValue(int, int), Constant Field Values

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:

getTimeScaleValue(int, int), Constant Field Values

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:

getTimeScaleValue(int, int), Constant Field Values

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:

getTimeScaleValue(int, int), Constant Field Values

EPOCH_OFFSET_MINUS_1_VALUE

@Deprecated
public static final int EPOCH_OFFSET_MINUS_1_VALUE

Deprecated. This API is ICU internal only.

The constant used to select the epoch offset minus 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 minus one.

See Also:

getTimeScaleValue(int, int), Constant Field Values

UNITS_ROUND_VALUE

@Deprecated
public static final int UNITS_ROUND_VALUE

Deprecated. This API is ICU internal only.

The constant used to select the units round value for a time scale. NOTE: This is an internal value. DO NOT USE IT.

See Also:

getTimeScaleValue(int, int), Constant Field Values

MIN_ROUND_VALUE

@Deprecated
public static final int MIN_ROUND_VALUE

Deprecated. This API is ICU internal only.

The constant used to select the minimum safe rounding value for a time scale. NOTE: This is an internal value. DO NOT USE IT.

See Also:

getTimeScaleValue(int, int), Constant Field Values

MAX_ROUND_VALUE

@Deprecated
public static final int MAX_ROUND_VALUE

Deprecated. This API is ICU internal only.

The constant used to select the maximum safe rounding value for a time scale. NOTE: This is an internal value. DO NOT USE IT.

See Also:

getTimeScaleValue(int, int), Constant Field Values

MAX_SCALE_VALUE

@Deprecated
public static final int MAX_SCALE_VALUE

Deprecated. This API is ICU internal only.

The number of time scale values. NOTE: This is an internal value. DO NOT USE IT.

See Also:

getTimeScaleValue(int, int), Constant Field Values

Method Detail

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 - The long datetime

timeScale - The time scale to convert from

Returns:

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 - The double datetime

timeScale - The time scale to convert from

Returns:

The datetime converted to the universal time scale

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 - The long datetime

timeScale - The time scale to convert from

Returns:

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 - The BigDecimal datetime

timeScale - The time scale to convert from

Returns:

The datetime converted to the universal 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 - The datetime in the universal time scale

timeScale - The time scale to convert to

Returns:

The datetime converted to the given time scale

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 - The datetime in the universal time scale

timeScale - The time scale to convert to

Returns:

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 - The datetime in the universal time scale

timeScale - The time scale to convert to

Returns:

The datetime converted to the given time scale

getTimeScaleValue

public static long getTimeScaleValue(int scale,
                                     int value)

Get a value associated with a particular time scale.

Parameters:

scale - - the time scale

value - - a constant representing the value to get

Returns:

- the value.

toBigDecimalTrunc

@Deprecated
public static BigDecimal toBigDecimalTrunc(BigDecimal universalTime,
                                                       int timeScale)

Deprecated. This API is ICU internal only.

Convert a time in the Universal Time Scale into another time scale. The division used to do the conversion rounds down. NOTE: This is an internal routine used by the tool that generates the to and from limits. Use it at your own risk.

Parameters:

universalTime - the time in the Universal Time scale

timeScale - the time scale to convert to

Returns:

the time in the given time scale