org.threeten.bp
Class YearMonth

java.lang.Object
  org.threeten.bp.jdk8.DefaultInterfaceTemporalAccessor
      org.threeten.bp.YearMonth

All Implemented Interfaces:

Serializable, Comparable<YearMonth>, Temporal, TemporalAccessor, TemporalAdjuster

public final class YearMonth
extends DefaultInterfaceTemporalAccessor
implements Temporal, TemporalAdjuster, Comparable<YearMonth>, Serializable

A year-month in the ISO-8601 calendar system, such as 2007-12.

YearMonth is an immutable date-time object that represents the combination of a year and month. Any field that can be derived from a year and month, such as quarter-of-year, can be obtained.

This class does not store or represent a day, time or time-zone. For example, the value "October 2007" can be stored in a YearMonth.

The ISO-8601 calendar system is the modern civil calendar system used today in most of the world. It is equivalent to the proleptic Gregorian calendar system, in which today's rules for leap years are applied for all time. For most applications written today, the ISO-8601 rules are entirely suitable. However, any application that makes use of historical dates, and requires them to be accurate will find the ISO-8601 approach unsuitable.

Specification for implementors

See Also:

Serialized Form

FROM

public static final TemporalQuery<YearMonth> FROM

Simulate JDK 8 method reference YearMonth::from.

now

public static YearMonth now()

Obtains the current year-month from the system clock in the default time-zone.

This will query the system clock in the default time-zone to obtain the current year-month. The zone and offset will be set based on the time-zone in the clock.

Using this method will prevent the ability to use an alternate clock for testing because the clock is hard-coded.

Returns:

the current year-month using the system clock and default time-zone, not null

now

public static YearMonth now(ZoneId zone)

Obtains the current year-month from the system clock in the specified time-zone.

This will query the system clock to obtain the current year-month. Specifying the time-zone avoids dependence on the default time-zone.

Using this method will prevent the ability to use an alternate clock for testing because the clock is hard-coded.

Parameters:

zone - the zone ID to use, not null

Returns:

the current year-month using the system clock, not null

now

public static YearMonth now(Clock clock)

Obtains the current year-month from the specified clock.

This will query the specified clock to obtain the current year-month. Using this method allows the use of an alternate clock for testing. The alternate clock may be introduced using dependency injection.

Parameters:

clock - the clock to use, not null

Returns:

the current year-month, not null

of

public static YearMonth of(int year,
                           Month month)

Obtains an instance of YearMonth from a year and month.

Parameters:

year - the year to represent, from MIN_YEAR to MAX_YEAR

month - the month-of-year to represent, not null

Returns:

the year-month, not null

Throws:

DateTimeException - if the year value is invalid

of

public static YearMonth of(int year,
                           int month)

Obtains an instance of YearMonth from a year and month.

Parameters:

year - the year to represent, from MIN_YEAR to MAX_YEAR

month - the month-of-year to represent, from 1 (January) to 12 (December)

Returns:

the year-month, not null

Throws:

DateTimeException - if either field value is invalid

from

public static YearMonth from(TemporalAccessor temporal)

Obtains an instance of YearMonth from a temporal object.

A TemporalAccessor represents some form of date and time information. This factory converts the arbitrary temporal object to an instance of YearMonth.

The conversion extracts the YEAR and MONTH_OF_YEAR fields. The extraction is only permitted if the temporal object has an ISO chronology, or can be converted to a LocalDate.

This method matches the signature of the functional interface TemporalQuery allowing it to be used in queries via method reference, YearMonth::from.

Parameters:

temporal - the temporal object to convert, not null

Returns:

the year-month, not null

Throws:

DateTimeException - if unable to convert to a YearMonth

parse

public static YearMonth parse(CharSequence text)

Obtains an instance of YearMonth from a text string such as 2007-12.

The string must represent a valid year-month. The format must be yyyy-MM. Years outside the range 0000 to 9999 must be prefixed by the plus or minus symbol.

Parameters:

text - the text to parse such as "2007-12", not null

Returns:

the parsed year-month, not null

Throws:

DateTimeParseException - if the text cannot be parsed

parse

public static YearMonth parse(CharSequence text,
                              DateTimeFormatter formatter)

Obtains an instance of YearMonth from a text string using a specific formatter.

The text is parsed using the formatter, returning a year-month.

Parameters:

text - the text to parse, not null

formatter - the formatter to use, not null

Returns:

the parsed year-month, not null

Throws:

DateTimeParseException - if the text cannot be parsed

isSupported

public boolean isSupported(TemporalField field)

Checks if the specified field is supported.

This checks if this year-month can be queried for the specified field. If false, then calling the range and get methods will throw an exception.

If the field is a ChronoField then the query is implemented here. The supported fields will return valid values based on this date-time. The supported fields are:

• MONTH_OF_YEAR
• EPOCH_MONTH
• YEAR_OF_ERA
• YEAR
• ERA

All other ChronoField instances will return false.

If the field is not a ChronoField, then the result of this method is obtained by invoking TemporalField.isSupportedBy(TemporalAccessor) passing this as the argument. Whether the field is supported is determined by the field.

Specified by:

isSupported in interface TemporalAccessor

Parameters:

field - the field to check, null returns false

Returns:

true if the field is supported on this year-month, false if not

isSupported

public boolean isSupported(TemporalUnit unit)

Description copied from interface: Temporal

Checks if the specified unit is supported.

This checks if the date-time can be queried for the specified unit. If false, then calling the plus and minus methods will throw an exception.

Specification for implementors

Implementations must check and handle all fields defined in ChronoUnit. If the field is supported, then true is returned, otherwise false

If the field is not a ChronoUnit, then the result of this method is obtained by invoking TemporalUnit.isSupportedBy(Temporal) passing this as the argument.

Implementations must not alter this object.

Specified by:

isSupported in interface Temporal

Parameters:

unit - the unit to check, null returns false

Returns:

true if this date-time can be queried for the unit, false if not

range

public ValueRange range(TemporalField field)

Gets the range of valid values for the specified field.

The range object expresses the minimum and maximum valid values for a field. This year-month is used to enhance the accuracy of the returned range. If it is not possible to return the range, because the field is not supported or for some other reason, an exception is thrown.

If the field is a ChronoField then the query is implemented here. The supported fields will return appropriate range instances. All other ChronoField instances will throw a DateTimeException.

If the field is not a ChronoField, then the result of this method is obtained by invoking TemporalField.rangeRefinedBy(TemporalAccessor) passing this as the argument. Whether the range can be obtained is determined by the field.

Specified by:

range in interface TemporalAccessor

Overrides:

range in class DefaultInterfaceTemporalAccessor

Parameters:

field - the field to query the range for, not null

Returns:

the range of valid values for the field, not null

Throws:

DateTimeException - if the range for the field cannot be obtained

get

public int get(TemporalField field)

Gets the value of the specified field from this year-month as an int.

This queries this year-month for the value for the specified field. The returned value will always be within the valid range of values for the field. If it is not possible to return the value, because the field is not supported or for some other reason, an exception is thrown.

If the field is a ChronoField then the query is implemented here. The supported fields will return valid values based on this year-month, except EPOCH_MONTH which is too large to fit in an int and throw a DateTimeException. All other ChronoField instances will throw a DateTimeException.

If the field is not a ChronoField, then the result of this method is obtained by invoking TemporalField.getFrom(TemporalAccessor) passing this as the argument. Whether the value can be obtained, and what the value represents, is determined by the field.

Specified by:

get in interface TemporalAccessor

Overrides:

get in class DefaultInterfaceTemporalAccessor

Parameters:

field - the field to get, not null

Returns:

the value for the field

Throws:

DateTimeException - if a value for the field cannot be obtained

ArithmeticException - if numeric overflow occurs

getLong

public long getLong(TemporalField field)

Gets the value of the specified field from this year-month as a long.

This queries this year-month for the value for the specified field. If it is not possible to return the value, because the field is not supported or for some other reason, an exception is thrown.

If the field is a ChronoField then the query is implemented here. The supported fields will return valid values based on this year-month. All other ChronoField instances will throw a DateTimeException.

If the field is not a ChronoField, then the result of this method is obtained by invoking TemporalField.getFrom(TemporalAccessor) passing this as the argument. Whether the value can be obtained, and what the value represents, is determined by the field.

Specified by:

getLong in interface TemporalAccessor

Parameters:

field - the field to get, not null

Returns:

the value for the field

Throws:

DateTimeException - if a value for the field cannot be obtained

ArithmeticException - if numeric overflow occurs

getYear

public int getYear()

Gets the year field.

This method returns the primitive int value for the year.

The year returned by this method is proleptic as per get(YEAR).

Returns:

the year, from MIN_YEAR to MAX_YEAR

getMonthValue

public int getMonthValue()

Gets the month-of-year field from 1 to 12.

This method returns the month as an int from 1 to 12. Application code is frequently clearer if the enum Month is used by calling getMonth().

Returns:

the month-of-year, from 1 to 12

See Also:

getMonth()

getMonth

public Month getMonth()

Gets the month-of-year field using the Month enum.

This method returns the enum Month for the month. This avoids confusion as to what int values mean. If you need access to the primitive int value then the enum provides the int value.

Returns:

the month-of-year, not null

isLeapYear

public boolean isLeapYear()

Checks if the year is a leap year, according to the ISO proleptic calendar system rules.

This method applies the current rules for leap years across the whole time-line. In general, a year is a leap year if it is divisible by four without remainder. However, years divisible by 100, are not leap years, with the exception of years divisible by 400 which are.

For example, 1904 is a leap year it is divisible by 4. 1900 was not a leap year as it is divisible by 100, however 2000 was a leap year as it is divisible by 400.

The calculation is proleptic - applying the same rules into the far future and far past. This is historically inaccurate, but is correct for the ISO-8601 standard.

Returns:

true if the year is leap, false otherwise

isValidDay

public boolean isValidDay(int dayOfMonth)

Checks if the day-of-month is valid for this year-month.

This method checks whether this year and month and the input day form a valid date.

Parameters:

dayOfMonth - the day-of-month to validate, from 1 to 31, invalid value returns false

Returns:

true if the day is valid for this year-month

lengthOfMonth

public int lengthOfMonth()

Returns the length of the month, taking account of the year.

This returns the length of the month in days. For example, a date in January would return 31.

Returns:

the length of the month in days, from 28 to 31

lengthOfYear

public int lengthOfYear()

Returns the length of the year.

This returns the length of the year in days, either 365 or 366.

Returns:

366 if the year is leap, 365 otherwise

with

public YearMonth with(TemporalAdjuster adjuster)

Returns an adjusted copy of this year-month.

This returns a new YearMonth, based on this one, with the year-month adjusted. The adjustment takes place using the specified adjuster strategy object. Read the documentation of the adjuster to understand what adjustment will be made.

A simple adjuster might simply set the one of the fields, such as the year field. A more complex adjuster might set the year-month to the next month that Halley's comet will pass the Earth.

The result of this method is obtained by invoking the TemporalAdjuster.adjustInto(Temporal) method on the specified adjuster passing this as the argument.

This instance is immutable and unaffected by this method call.

Specified by:

with in interface Temporal

Parameters:

adjuster - the adjuster to use, not null

Returns:

a YearMonth based on this with the adjustment made, not null

Throws:

DateTimeException - if the adjustment cannot be made

ArithmeticException - if numeric overflow occurs

with

public YearMonth with(TemporalField field,
                      long newValue)

Returns a copy of this year-month with the specified field set to a new value.

This returns a new YearMonth, based on this one, with the value for the specified field changed. This can be used to change any supported field, such as the year or month. If it is not possible to set the value, because the field is not supported or for some other reason, an exception is thrown.

If the field is a ChronoField then the adjustment is implemented here. The supported fields behave as follows:

• MONTH_OF_YEAR - Returns a YearMonth with the specified month-of-year. The year will be unchanged.
• PROLEPTIC_MONTH - Returns a YearMonth with the specified proleptic-month. This completely replaces the year and month of this object.
• YEAR_OF_ERA - Returns a YearMonth with the specified year-of-era The month and era will be unchanged.
• YEAR - Returns a YearMonth with the specified year. The month will be unchanged.
• ERA - Returns a YearMonth with the specified era. The month and year-of-era will be unchanged.

In all cases, if the new value is outside the valid range of values for the field then a DateTimeException will be thrown.

All other ChronoField instances will throw a DateTimeException.

If the field is not a ChronoField, then the result of this method is obtained by invoking TemporalField.adjustInto(Temporal, long) passing this as the argument. In this case, the field determines whether and how to adjust the instant.

This instance is immutable and unaffected by this method call.

Specified by:

with in interface Temporal

Parameters:

field - the field to set in the result, not null

newValue - the new value of the field in the result

Returns:

a YearMonth based on this with the specified field set, not null

Throws:

DateTimeException - if the field cannot be set

ArithmeticException - if numeric overflow occurs

withYear

public YearMonth withYear(int year)

Returns a copy of this YearMonth with the year altered.

This instance is immutable and unaffected by this method call.

Parameters:

year - the year to set in the returned year-month, from MIN_YEAR to MAX_YEAR

Returns:

a YearMonth based on this year-month with the requested year, not null

Throws:

DateTimeException - if the year value is invalid

withMonth

public YearMonth withMonth(int month)

Returns a copy of this YearMonth with the month-of-year altered.

This instance is immutable and unaffected by this method call.

Parameters:

month - the month-of-year to set in the returned year-month, from 1 (January) to 12 (December)

Returns:

a YearMonth based on this year-month with the requested month, not null

Throws:

DateTimeException - if the month-of-year value is invalid

plus

public YearMonth plus(TemporalAmount amount)

Returns a copy of this year-month with the specified period added.

This method returns a new year-month based on this year-month with the specified period added. The adder is typically Period but may be any other type implementing the TemporalAmount interface. The calculation is delegated to the specified adjuster, which typically calls back to plus(long, TemporalUnit).

This instance is immutable and unaffected by this method call.

Specified by:

plus in interface Temporal

Parameters:

amount - the amount to add, not null

Returns:

a YearMonth based on this year-month with the addition made, not null

Throws:

DateTimeException - if the addition cannot be made

ArithmeticException - if numeric overflow occurs

plus

public YearMonth plus(long amountToAdd,
                      TemporalUnit unit)

Returns an object of the same type as this object with the specified period added.

This method returns a new object based on this one with the specified period added. For example, on a LocalDate, this could be used to add a number of years, months or days. The returned object will have the same observable type as this object.

In some cases, changing a field is not fully defined. For example, if the target object is a date representing the 31st January, then adding one month would be unclear. In cases like this, the field is responsible for resolving the result. Typically it will choose the previous valid date, which would be the last valid day of February in this example.

If the implementation represents a date-time that has boundaries, such as LocalTime, then the permitted units must include the boundary unit, but no multiples of the boundary unit. For example, LocalTime must accept DAYS but not WEEKS or MONTHS.

Specification for implementors

Implementations must check and handle all units defined in ChronoUnit. If the unit is supported, then the addition must be performed. If unsupported, then a DateTimeException must be thrown.

If the unit is not a ChronoUnit, then the result of this method is obtained by invoking TemporalUnit.addTo(Temporal, long) passing this as the first argument.

Implementations must not alter either this object or the specified temporal object. Instead, an adjusted copy of the original must be returned. This provides equivalent, safe behavior for immutable and mutable implementations.

Specified by:

plus in interface Temporal

Parameters:

amountToAdd - the amount of the specified unit to add, may be negative

unit - the unit of the period to add, not null

Returns:

an object of the same type with the specified period added, not null

Throws:

DateTimeException - if the unit cannot be added

ArithmeticException - if numeric overflow occurs

plusYears

public YearMonth plusYears(long yearsToAdd)

Returns a copy of this year-month with the specified period in years added.

This instance is immutable and unaffected by this method call.

Parameters:

yearsToAdd - the years to add, may be negative

Returns:

a YearMonth based on this year-month with the years added, not null

Throws:

DateTimeException - if the result exceeds the supported range

plusMonths

public YearMonth plusMonths(long monthsToAdd)

Returns a copy of this year-month with the specified period in months added.

This instance is immutable and unaffected by this method call.

Parameters:

monthsToAdd - the months to add, may be negative

Returns:

a YearMonth based on this year-month with the months added, not null

Throws:

DateTimeException - if the result exceeds the supported range

minus

public YearMonth minus(TemporalAmount amount)

Returns a copy of this year-month with the specified period subtracted.

This method returns a new year-month based on this year-month with the specified period subtracted. The subtractor is typically Period but may be any other type implementing the TemporalAmount interface. The calculation is delegated to the specified adjuster, which typically calls back to minus(long, TemporalUnit).

This instance is immutable and unaffected by this method call.

Specified by:

minus in interface Temporal

Parameters:

amount - the amount to aubtract, not null

Returns:

a YearMonth based on this year-month with the subtraction made, not null

Throws:

DateTimeException - if the subtraction cannot be made

ArithmeticException - if numeric overflow occurs

minus

public YearMonth minus(long amountToSubtract,
                       TemporalUnit unit)

Returns an object of the same type as this object with the specified period subtracted.

This method returns a new object based on this one with the specified period subtracted. For example, on a LocalDate, this could be used to subtract a number of years, months or days. The returned object will have the same observable type as this object.

In some cases, changing a field is not fully defined. For example, if the target object is a date representing the 31st March, then subtracting one month would be unclear. In cases like this, the field is responsible for resolving the result. Typically it will choose the previous valid date, which would be the last valid day of February in this example.

If the implementation represents a date-time that has boundaries, such as LocalTime, then the permitted units must include the boundary unit, but no multiples of the boundary unit. For example, LocalTime must accept DAYS but not WEEKS or MONTHS.

Specification for implementors

Implementations must behave in a manor equivalent to the default method behavior.

Implementations must not alter either this object or the specified temporal object. Instead, an adjusted copy of the original must be returned. This provides equivalent, safe behavior for immutable and mutable implementations.

Specified by:

minus in interface Temporal

Parameters:

amountToSubtract - the amount of the specified unit to subtract, may be negative

unit - the unit of the period to subtract, not null

Returns:

an object of the same type with the specified period subtracted, not null

Throws:

DateTimeException - if the unit cannot be subtracted

ArithmeticException - if numeric overflow occurs

minusYears

public YearMonth minusYears(long yearsToSubtract)

Returns a copy of this year-month with the specified period in years subtracted.

This instance is immutable and unaffected by this method call.

Parameters:

yearsToSubtract - the years to subtract, may be negative

Returns:

a YearMonth based on this year-month with the years subtracted, not null

Throws:

DateTimeException - if the result exceeds the supported range

minusMonths

public YearMonth minusMonths(long monthsToSubtract)

Returns a copy of this year-month with the specified period in months subtracted.

This instance is immutable and unaffected by this method call.

Parameters:

monthsToSubtract - the months to subtract, may be negative

Returns:

a YearMonth based on this year-month with the months subtracted, not null

Throws:

DateTimeException - if the result exceeds the supported range

query

public <R> R query(TemporalQuery<R> query)

Queries this year-month using the specified query.

This queries this year-month using the specified query strategy object. The TemporalQuery object defines the logic to be used to obtain the result. Read the documentation of the query to understand what the result of this method will be.

The result of this method is obtained by invoking the TemporalQuery.queryFrom(TemporalAccessor) method on the specified query passing this as the argument.

Specified by:

query in interface TemporalAccessor

Overrides:

query in class DefaultInterfaceTemporalAccessor

Type Parameters:

R - the type of the result

Parameters:

query - the query to invoke, not null

Returns:

the query result, null may be returned (defined by the query)

Throws:

DateTimeException - if unable to query (defined by the query)

ArithmeticException - if numeric overflow occurs (defined by the query)

adjustInto

public Temporal adjustInto(Temporal temporal)

Adjusts the specified temporal object to have this year-month.

This returns a temporal object of the same observable type as the input with the year and month changed to be the same as this.

The adjustment is equivalent to using Temporal.with(TemporalField, long) passing ChronoField.PROLEPTIC_MONTH as the field. If the specified temporal object does not use the ISO calendar system then a DateTimeException is thrown.

In most cases, it is clearer to reverse the calling pattern by using Temporal.with(TemporalAdjuster):

   // these two lines are equivalent, but the second approach is recommended
   temporal = thisYearMonth.adjustInto(temporal);
   temporal = temporal.with(thisYearMonth);
 

This instance is immutable and unaffected by this method call.

Specified by:

adjustInto in interface TemporalAdjuster

Parameters:

temporal - the target object to be adjusted, not null

Returns:

the adjusted object, not null

Throws:

DateTimeException - if unable to make the adjustment

ArithmeticException - if numeric overflow occurs

until

public long until(Temporal endExclusive,
                  TemporalUnit unit)

Calculates the period between this year-month and another year-month in terms of the specified unit.

This calculates the period between two year-months in terms of a single unit. The start and end points are this and the specified year-month. The result will be negative if the end is before the start. The Temporal passed to this method must be a YearMonth. For example, the period in years between two year-months can be calculated using startYearMonth.until(endYearMonth, YEARS).

The calculation returns a whole number, representing the number of complete units between the two year-months. For example, the period in decades between 2012-06 and 2032-05 will only be one decade as it is one month short of two decades.

This method operates in association with TemporalUnit.between(org.threeten.bp.temporal.Temporal, org.threeten.bp.temporal.Temporal). The result of this method is a long representing the amount of the specified unit. By contrast, the result of between is an object that can be used directly in addition/subtraction:

   long period = start.until(end, YEARS);   // this method
   dateTime.plus(YEARS.between(start, end));      // use in plus/minus
 

The calculation is implemented in this method for ChronoUnit. The units MONTHS, YEARS, DECADES, CENTURIES, MILLENNIA and ERAS are supported. Other ChronoUnit values will throw an exception.

If the unit is not a ChronoUnit, then the result of this method is obtained by invoking TemporalUnit.between(Temporal, Temporal) passing this as the first argument and the input temporal as the second argument.

This instance is immutable and unaffected by this method call.

Specified by:

until in interface Temporal

Parameters:

endExclusive - the end year-month, which is converted to a YearMonth, not null

unit - the unit to measure the period in, not null

Returns:

the amount of the period between this year-month and the end year-month

Throws:

DateTimeException - if the period cannot be calculated

ArithmeticException - if numeric overflow occurs

atDay

public LocalDate atDay(int dayOfMonth)

Combines this year-month with a day-of-month to create a LocalDate.

This returns a LocalDate formed from this year-month and the specified day-of-month.

The day-of-month value must be valid for the year-month.

This method can be used as part of a chain to produce a date:

  LocalDate date = year.atMonth(month).atDay(day);
 

Parameters:

dayOfMonth - the day-of-month to use, from 1 to 31

Returns:

the date formed from this year-month and the specified day, not null

Throws:

DateTimeException - if the day is invalid for the year-month

See Also:

isValidDay(int)

atEndOfMonth

public LocalDate atEndOfMonth()

Returns a LocalDate at the end of the month.

This returns a LocalDate based on this year-month. The day-of-month is set to the last valid day of the month, taking into account leap years.

This method can be used as part of a chain to produce a date:

  LocalDate date = year.atMonth(month).atEndOfMonth();
 

Returns:

the last valid date of this year-month, not null

compareTo

public int compareTo(YearMonth other)

Compares this year-month to another year-month.

The comparison is based first on the value of the year, then on the value of the month. It is "consistent with equals", as defined by Comparable.

Specified by:

compareTo in interface Comparable<YearMonth>

Parameters:

other - the other year-month to compare to, not null

Returns:

the comparator value, negative if less, positive if greater

isAfter

public boolean isAfter(YearMonth other)

Is this year-month after the specified year-month.

Parameters:

other - the other year-month to compare to, not null

Returns:

true if this is after the specified year-month

isBefore

public boolean isBefore(YearMonth other)

Is this year-month before the specified year-month.

Parameters:

other - the other year-month to compare to, not null

Returns:

true if this point is before the specified year-month

equals

public boolean equals(Object obj)

Checks if this year-month is equal to another year-month.

The comparison is based on the time-line position of the year-months.

Overrides:

equals in class Object

Parameters:

obj - the object to check, null returns false

Returns:

true if this is equal to the other year-month

hashCode

public int hashCode()

A hash code for this year-month.

Overrides:

hashCode in class Object

Returns:

a suitable hash code

toString

public String toString()

Outputs this year-month as a String, such as 2007-12.

The output will be in the format yyyy-MM:

Overrides:

toString in class Object

Returns:

a string representation of this year-month, not null

format

public String format(DateTimeFormatter formatter)

Outputs this year-month as a String using the formatter.

This year-month will be passed to the formatter print method.

Parameters:

formatter - the formatter to use, not null

Returns:

the formatted year-month string, not null

Throws:

DateTimeException - if an error occurs during printing