added in API level 26

YearMonth

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

java.lang.Object
   ↳ java.time.YearMonth


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.

Summary

Public methods

Temporal adjustInto(Temporal temporal)

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

LocalDate atDay(int dayOfMonth)

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

LocalDate atEndOfMonth()

Returns a LocalDate at the end of the month.

int compareTo(YearMonth other)

Compares this year-month to another year-month.

boolean equals(Object obj)

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

String format(DateTimeFormatter formatter)

Formats this year-month using the specified formatter.

static YearMonth from(TemporalAccessor temporal)

Obtains an instance of YearMonth from a temporal object.

int get(TemporalField field)

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

long getLong(TemporalField field)

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

Month getMonth()

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

int getMonthValue()

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

int getYear()

Gets the year field.

int hashCode()

A hash code for this year-month.

boolean isAfter(YearMonth other)

Checks if this year-month is after the specified year-month.

boolean isBefore(YearMonth other)

Checks if this year-month is before the specified year-month.

boolean isLeapYear()

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

boolean isSupported(TemporalUnit unit)

Checks if the specified unit is supported.

boolean isSupported(TemporalField field)

Checks if the specified field is supported.

boolean isValidDay(int dayOfMonth)

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

int lengthOfMonth()

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

int lengthOfYear()

Returns the length of the year.

YearMonth minus(TemporalAmount amountToSubtract)

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

YearMonth minus(long amountToSubtract, TemporalUnit unit)

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

YearMonth minusMonths(long monthsToSubtract)

Returns a copy of this YearMonth with the specified number of months subtracted.

YearMonth minusYears(long yearsToSubtract)

Returns a copy of this YearMonth with the specified number of years subtracted.

static YearMonth now(ZoneId zone)

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

static YearMonth now()

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

static YearMonth now(Clock clock)

Obtains the current year-month from the specified clock.

static YearMonth of(int year, Month month)

Obtains an instance of YearMonth from a year and month.

static YearMonth of(int year, int month)

Obtains an instance of YearMonth from a year and month.

static YearMonth parse(CharSequence text, DateTimeFormatter formatter)

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

static YearMonth parse(CharSequence text)

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

YearMonth plus(TemporalAmount amountToAdd)

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

YearMonth plus(long amountToAdd, TemporalUnit unit)

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

YearMonth plusMonths(long monthsToAdd)

Returns a copy of this YearMonth with the specified number of months added.

YearMonth plusYears(long yearsToAdd)

Returns a copy of this YearMonth with the specified number of years added.

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

Queries this year-month using the specified query.

ValueRange range(TemporalField field)

Gets the range of valid values for the specified field.

String toString()

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

long until(Temporal endExclusive, TemporalUnit unit)

Calculates the amount of time until another year-month in terms of the specified unit.

YearMonth with(TemporalField field, long newValue)

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

YearMonth with(TemporalAdjuster adjuster)

Returns an adjusted copy of this year-month.

YearMonth withMonth(int month)

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

YearMonth withYear(int year)

Returns a copy of this YearMonth with the year altered.

Inherited methods

Public methods

adjustInto

added in API level 26
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.

Parameters
temporal Temporal: the target object to be adjusted, not null

Returns
Temporal the adjusted object, not null

Throws
DateTimeException if unable to make the adjustment
ArithmeticException if numeric overflow occurs

atDay

added in API level 26
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 int: the day-of-month to use, from 1 to 31

Returns
LocalDate 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:

atEndOfMonth

added in API level 26
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
LocalDate the last valid date of this year-month, not null

compareTo

added in API level 26
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.

Parameters
other YearMonth: the other year-month to compare to, not null

Returns
int the comparator value, negative if less, positive if greater

equals

added in API level 26
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.

Parameters
obj Object: the object to check, null returns false

Returns
boolean true if this is equal to the other year-month

format

added in API level 26
public String format (DateTimeFormatter formatter)

Formats this year-month using the specified formatter.

This year-month will be passed to the formatter to produce a string.

Parameters
formatter DateTimeFormatter: the formatter to use, not null

Returns
String the formatted year-month string, not null

Throws
DateTimeException if an error occurs during printing

from

added in API level 26
public static YearMonth from (TemporalAccessor temporal)

Obtains an instance of YearMonth from a temporal object.

This obtains a year-month based on the specified temporal. A TemporalAccessor represents an arbitrary set of date and time information, which this factory converts 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 as a query via method reference, YearMonth::from.

Parameters
temporal TemporalAccessor: the temporal object to convert, not null

Returns
YearMonth the year-month, not null

Throws
DateTimeException if unable to convert to a YearMonth

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 of 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 PROLEPTIC_MONTH which is too large to fit in an int and throw a DateTimeException. All other ChronoField instances will throw an UnsupportedTemporalTypeException.

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.

Parameters
field TemporalField: the field to get, not null

Returns
int the value for the field

Throws
DateTimeException if a value for the field cannot be obtained or the value is outside the range of valid values for the field
UnsupportedTemporalTypeException if the field is not supported or the range of values exceeds an int
ArithmeticException if numeric overflow occurs

getLong

added in API level 26
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 of 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 an UnsupportedTemporalTypeException.

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.

Parameters
field TemporalField: the field to get, not null

Returns
long the value for the field

Throws
DateTimeException if a value for the field cannot be obtained
UnsupportedTemporalTypeException if the field is not supported
ArithmeticException if numeric overflow occurs

getMonth

added in API level 26
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
Month the month-of-year, not null

See also:

getMonthValue

added in API level 26
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
int the month-of-year, from 1 to 12

See also:

getYear

added in API level 26
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
int the year, from MIN_YEAR to MAX_YEAR

hashCode

added in API level 26
public int hashCode ()

A hash code for this year-month.

Returns
int a suitable hash code

isAfter

added in API level 26
public boolean isAfter (YearMonth other)

Checks if this year-month is after the specified year-month.

Parameters
other YearMonth: the other year-month to compare to, not null

Returns
boolean true if this is after the specified year-month

isBefore

added in API level 26
public boolean isBefore (YearMonth other)

Checks if this year-month is before the specified year-month.

Parameters
other YearMonth: the other year-month to compare to, not null

Returns
boolean true if this point is before the specified year-month

isLeapYear

added in API level 26
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
boolean true if the year is leap, false otherwise

isSupported

added in API level 26
public boolean isSupported (TemporalUnit unit)

Checks if the specified unit is supported.

This checks if the specified unit can be added to, or subtracted from, this year-month. If false, then calling the plus(long, TemporalUnit) and minus methods will throw an exception.

If the unit is a ChronoUnit then the query is implemented here. The supported units are:

  • MONTHS
  • YEARS
  • DECADES
  • CENTURIES
  • MILLENNIA
  • ERAS
All other ChronoUnit instances will return false.

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

Parameters
unit TemporalUnit: the unit to check, null returns false

Returns
boolean true if the unit can be added/subtracted, false if not

isSupported

added in API level 26
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, get and with(TemporalField, long) methods will throw an exception.

If the field is a ChronoField then the query is implemented here. The supported fields are:

  • MONTH_OF_YEAR
  • PROLEPTIC_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.

Parameters
field TemporalField: the field to check, null returns false

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

isValidDay

added in API level 26
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 int: the day-of-month to validate, from 1 to 31, invalid value returns false

Returns
boolean true if the day is valid for this year-month

lengthOfMonth

added in API level 26
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
int the length of the month in days, from 28 to 31

lengthOfYear

added in API level 26
public int lengthOfYear ()

Returns the length of the year.

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

Returns
int 366 if the year is leap, 365 otherwise

minus

added in API level 27
public YearMonth minus (TemporalAmount amountToSubtract)

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

This returns a YearMonth, based on this one, with the specified amount subtracted. The amount is typically Period but may be any other type implementing the TemporalAmount interface.

The calculation is delegated to the amount object by calling TemporalAmount.subtractFrom(Temporal). The amount implementation is free to implement the subtraction in any way it wishes, however it typically calls back to minus(long, TemporalUnit). Consult the documentation of the amount implementation to determine if it can be successfully subtracted.

This instance is immutable and unaffected by this method call.

Parameters
amountToSubtract TemporalAmount: the amount to subtract, not null

Returns
YearMonth 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

added in API level 27
public YearMonth minus (long amountToSubtract, 
                TemporalUnit unit)

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

This returns a YearMonth, based on this one, with the amount in terms of the unit subtracted. If it is not possible to subtract the amount, because the unit is not supported or for some other reason, an exception is thrown.

This method is equivalent to plus(long, TemporalUnit) with the amount negated. See that method for a full description of how addition, and thus subtraction, works.

This instance is immutable and unaffected by this method call.

Parameters
amountToSubtract long: the amount of the unit to subtract from the result, may be negative

unit TemporalUnit: the unit of the amount to subtract, not null

Returns
YearMonth a YearMonth based on this year-month with the specified amount subtracted, not null

Throws
DateTimeException if the subtraction cannot be made
UnsupportedTemporalTypeException if the unit is not supported
ArithmeticException if numeric overflow occurs

minusMonths

added in API level 26
public YearMonth minusMonths (long monthsToSubtract)

Returns a copy of this YearMonth with the specified number of months subtracted.

This instance is immutable and unaffected by this method call.

Parameters
monthsToSubtract long: the months to subtract, may be negative

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

Throws
DateTimeException if the result exceeds the supported range

minusYears

added in API level 26
public YearMonth minusYears (long yearsToSubtract)

Returns a copy of this YearMonth with the specified number of years subtracted.

This instance is immutable and unaffected by this method call.

Parameters
yearsToSubtract long: the years to subtract, may be negative

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

Throws
DateTimeException if the result exceeds the supported range

now

added in API level 26
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 ZoneId: the zone ID to use, not null

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

now

added in API level 26
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.

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

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

now

added in API level 26
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 Clock: the clock to use, not null

Returns
YearMonth the current year-month, not null

of

added in API level 26
public static YearMonth of (int year, 
                Month month)

Obtains an instance of YearMonth from a year and month.

Parameters
year int: the year to represent, from MIN_YEAR to MAX_YEAR

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

Returns
YearMonth the year-month, not null

Throws
DateTimeException if the year value is invalid

of

added in API level 26
public static YearMonth of (int year, 
                int month)

Obtains an instance of YearMonth from a year and month.

Parameters
year int: the year to represent, from MIN_YEAR to MAX_YEAR

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

Returns
YearMonth the year-month, not null

Throws
DateTimeException if either field value is invalid

parse

added in API level 26
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 CharSequence: the text to parse, not null

formatter DateTimeFormatter: the formatter to use, not null

Returns
YearMonth the parsed year-month, not null

Throws
DateTimeParseException if the text cannot be parsed

parse

added in API level 26
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 uuuu-MM. Years outside the range 0000 to 9999 must be prefixed by the plus or minus symbol.

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

Returns
YearMonth the parsed year-month, not null

Throws
DateTimeParseException if the text cannot be parsed

plus

added in API level 27
public YearMonth plus (TemporalAmount amountToAdd)

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

This returns a YearMonth, based on this one, with the specified amount added. The amount is typically Period but may be any other type implementing the TemporalAmount interface.

The calculation is delegated to the amount object by calling TemporalAmount.addTo(Temporal). The amount implementation is free to implement the addition in any way it wishes, however it typically calls back to plus(long, TemporalUnit). Consult the documentation of the amount implementation to determine if it can be successfully added.

This instance is immutable and unaffected by this method call.

Parameters
amountToAdd TemporalAmount: the amount to add, not null

Returns
YearMonth 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

added in API level 26
public YearMonth plus (long amountToAdd, 
                TemporalUnit unit)

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

This returns a YearMonth, based on this one, with the amount in terms of the unit added. If it is not possible to add the amount, because the unit is not supported or for some other reason, an exception is thrown.

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

  • MONTHS - Returns a YearMonth with the specified number of months added. This is equivalent to plusMonths(long).
  • YEARS - Returns a YearMonth with the specified number of years added. This is equivalent to plusYears(long).
  • DECADES - Returns a YearMonth with the specified number of decades added. This is equivalent to calling plusYears(long) with the amount multiplied by 10.
  • CENTURIES - Returns a YearMonth with the specified number of centuries added. This is equivalent to calling plusYears(long) with the amount multiplied by 100.
  • MILLENNIA - Returns a YearMonth with the specified number of millennia added. This is equivalent to calling plusYears(long) with the amount multiplied by 1,000.
  • ERAS - Returns a YearMonth with the specified number of eras added. Only two eras are supported so the amount must be one, zero or minus one. If the amount is non-zero then the year is changed such that the year-of-era is unchanged.

All other ChronoUnit instances will throw an UnsupportedTemporalTypeException.

If the field is not a ChronoUnit, then the result of this method is obtained by invoking TemporalUnit.addTo(Temporal, long) passing this as the argument. In this case, the unit determines whether and how to perform the addition.

This instance is immutable and unaffected by this method call.

Parameters
amountToAdd long: the amount of the unit to add to the result, may be negative

unit TemporalUnit: the unit of the amount to add, not null

Returns
YearMonth a YearMonth based on this year-month with the specified amount added, not null

Throws
DateTimeException if the addition cannot be made
UnsupportedTemporalTypeException if the unit is not supported
ArithmeticException if numeric overflow occurs

plusMonths

added in API level 26
public YearMonth plusMonths (long monthsToAdd)

Returns a copy of this YearMonth with the specified number of months added.

This instance is immutable and unaffected by this method call.

Parameters
monthsToAdd long: the months to add, may be negative

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

Throws
DateTimeException if the result exceeds the supported range

plusYears

added in API level 26
public YearMonth plusYears (long yearsToAdd)

Returns a copy of this YearMonth with the specified number of years added.

This instance is immutable and unaffected by this method call.

Parameters
yearsToAdd long: the years to add, may be negative

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

Throws
DateTimeException if the result exceeds the supported range

query

public 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.

Parameters
query TemporalQuery: the query to invoke, not null

Returns
R 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)

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 an UnsupportedTemporalTypeException.

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.

Parameters
field TemporalField: the field to query the range for, not null

Returns
ValueRange the range of valid values for the field, not null

Throws
DateTimeException if the range for the field cannot be obtained
UnsupportedTemporalTypeException if the field is not supported

toString

added in API level 26
public String toString ()

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

The output will be in the format uuuu-MM:

Returns
String a string representation of this year-month, not null

until

added in API level 26
public long until (Temporal endExclusive, 
                TemporalUnit unit)

Calculates the amount of time until another year-month in terms of the specified unit.

This calculates the amount of time between two YearMonth objects in terms of a single TemporalUnit. 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 is converted to a YearMonth using from(TemporalAccessor). For example, the amount 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 amount in decades between 2012-06 and 2032-05 will only be one decade as it is one month short of two decades.

There are two equivalent ways of using this method. The first is to invoke this method. The second is to use TemporalUnit.between(Temporal, Temporal):

   // these two lines are equivalent
   amount = start.until(end, MONTHS);
   amount = MONTHS.between(start, end);
 
The choice should be made based on which makes the code more readable.

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 converted input temporal as the second argument.

This instance is immutable and unaffected by this method call.

Parameters
endExclusive Temporal: the end date, exclusive, which is converted to a YearMonth, not null

unit TemporalUnit: the unit to measure the amount in, not null

Returns
long the amount of time between this year-month and the end year-month

Throws
DateTimeException if the amount cannot be calculated, or the end temporal cannot be converted to a YearMonth
UnsupportedTemporalTypeException if the unit is not supported
ArithmeticException if numeric overflow occurs

with

added in API level 26
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 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 an UnsupportedTemporalTypeException.

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.

Parameters
field TemporalField: the field to set in the result, not null

newValue long: the new value of the field in the result

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

Throws
DateTimeException if the field cannot be set
UnsupportedTemporalTypeException if the field is not supported
ArithmeticException if numeric overflow occurs

with

added in API level 27
public YearMonth with (TemporalAdjuster adjuster)

Returns an adjusted copy of this year-month.

This returns a 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.

Parameters
adjuster TemporalAdjuster: the adjuster to use, not null

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

Throws
DateTimeException if the adjustment cannot be made
ArithmeticException if numeric overflow occurs

withMonth

added in API level 26
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 int: the month-of-year to set in the returned year-month, from 1 (January) to 12 (December)

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

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

withYear

added in API level 26
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 int: the year to set in the returned year-month, from MIN_YEAR to MAX_YEAR

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

Throws
DateTimeException if the year value is invalid