TemporalQuery

  • TemporalQuery provides a strategy for extracting information from temporal objects, offering flexibility beyond TemporalField.

  • It allows for diverse query implementations, returning any data type, including custom objects or primitives.

  • While there are two usage approaches (direct invocation or via TemporalAccessor.query), the latter is recommended for code clarity.

  • Common implementations often leverage method references or are accessed as static methods within TemporalQueries.

  • The queryFrom method handles the querying logic, potentially returning null if the desired information isn't found.
public interface TemporalQuery

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);
It is recommended to use the second approach, query(TemporalQuery), as it is a lot clearer to read in code.

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

Public Method Summary

abstract R
queryFrom(TemporalAccessor temporal)
Queries the specified temporal object.

Public Methods

public abstract R queryFrom (TemporalAccessor temporal)

Queries the specified temporal object.

This queries the specified temporal object to return an object using the logic encapsulated in the implementing class. 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.

There are two equivalent ways of using this method. The first is to invoke this method 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);
It is recommended to use the second approach, query(TemporalQuery), as it is a lot clearer to read in code.

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