Interface TemporalQuery<R>

Strategy for querying a temporal object.

Queries are a key tool for extracting information from temporal objects. They exist to externalize the process of querying, permitting different approaches, as per the strategy design pattern. Examples might be a query that checks if the date is the day before February 29th in a leap year, or calculates the number of days to your next birthday.

The TemporalField interface provides another mechanism for querying temporal objects. That interface is limited to returning a long. By contrast, queries can return any type.

There are two equivalent ways of using a TemporalQuery. The first is to invoke the method on this interface directly. The second is to use TemporalAccessor.query(TemporalQuery):

// these two lines are equivalent, but the second approach is recommended
   temporal = thisQuery.queryFrom(temporal);
   temporal = temporal.query(thisQuery);

The most common implementations are method references, such as LocalDate::from and ZoneId::from. Additional common queries are provided as static methods in TemporalQueries.

Methods

queryFrom

R queryFrom(TemporalAccessor temporal)

// these two lines are equivalent, but the second approach is recommended
   temporal = thisQuery.queryFrom(temporal);
   temporal = temporal.query(thisQuery);

Implementation Requirements:

The implementation must take the input object and query it. The implementation defines the logic of the query and is responsible for documenting that logic. It may use any method on TemporalAccessor to determine the result. The input object must not be altered.

The input temporal object may be in a calendar system other than ISO. Implementations may choose to document compatibility with other calendar systems, or reject non-ISO temporal objects by querying the chronology.

This method may be called from multiple threads in parallel. It must be thread-safe when invoked.

Parameters:

temporal - the temporal object to query, not null

Returns:

the queried value, may return null to indicate not found

Throws:

DateTimeException - if unable to query

ArithmeticException - if numeric overflow occurs