Trail: Date Time
Lesson: Standard Calendar
Section: The Temporal Package

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Temporal Query

A TemporalQuery can be used to retrieve information from a temporal-based object.

Predefined Queries

The TemporalQueries class (note the plural) provides several predefined queries, including methods that are useful when the application cannot identify the type of temporal-based object. As with the adjusters, the predefined queries are defined as static methods and are designed to be used with the static import statement.

The precision query, for example, returns the smallest ChronoUnit that can be returned by a particular temporal-based object. The following example uses the precision query on several types of temporal-based objects:

TemporalQuery<TemporalUnit> query = TemporalQueries.precision();
System.out.printf("LocalDate precision is %s%n",
                  LocalDate.now().query(query));
System.out.printf("LocalDateTime precision is %s%n",
                  LocalDateTime.now().query(query));
System.out.printf("Year precision is %s%n",
                  Year.now().query(query));
System.out.printf("YearMonth precision is %s%n",
                  YearMonth.now().query(query));
System.out.printf("Instant precision is %s%n",
                  Instant.now().query(query));

The output looks like the following:

LocalDate precision is Days
LocalDateTime precision is Nanos
Year precision is Years
YearMonth precision is Months
Instant precision is Nanos

Custom Queries

You can also create your own custom queries. One way to do this is to create a class that implements the TemporalQuery interface with the queryFrom(TemporalAccessor) method. The CheckDate example implements two custom queries. The first custom query can be found in the FamilyVacations class, which implements the TemporalQuery interface. The queryFrom method compares the passed-in date against scheduled vacation dates and returns TRUE if it falls within those date ranges.

// Returns true if the passed-in date occurs during one of the
// family vacations. Because the query compares the month and day only,
// the check succeeds even if the Temporal types are not the same.
public Boolean queryFrom(TemporalAccessor date) {
    int month = date.get(ChronoField.MONTH_OF_YEAR);
    int day   = date.get(ChronoField.DAY_OF_MONTH);

    // Disneyland over Spring Break
    if ((month == Month.APRIL.getValue()) && ((day >= 3) && (day <= 8)))
        return Boolean.TRUE;

    // Smith family reunion on Lake Saugatuck
    if ((month == Month.AUGUST.getValue()) && ((day >= 8) && (day <= 14)))
        return Boolean.TRUE;

    return Boolean.FALSE;
}

The second custom query is implemented in the FamilyBirthdays class. This class provides an isFamilyBirthday method that compares the passed-in date against several birthdays and returns TRUE if there is a match.

// Returns true if the passed-in date is the same as one of the
// family birthdays. Because the query compares the month and day only,
// the check succeeds even if the Temporal types are not the same.
public static Boolean isFamilyBirthday(TemporalAccessor date) {
    int month = date.get(ChronoField.MONTH_OF_YEAR);
    int day   = date.get(ChronoField.DAY_OF_MONTH);

    // Angie's birthday is on April 3.
    if ((month == Month.APRIL.getValue()) && (day == 3))
        return Boolean.TRUE;

    // Sue's birthday is on June 18.
    if ((month == Month.JUNE.getValue()) && (day == 18))
        return Boolean.TRUE;

    // Joe's birthday is on May 29.
    if ((month == Month.MAY.getValue()) && (day == 29))
        return Boolean.TRUE;

    return Boolean.FALSE;
}

The FamilyBirthday class does not implement the TemporalQuery interface and can be used as part of a lambda expression. The following code, from the CheckDate example, shows how to invoke both custom queries.

// Invoking the query without using a lambda expression.
Boolean isFamilyVacation = date.query(new FamilyVacations());

// Invoking the query using a lambda expression.
Boolean isFamilyBirthday = date.query(FamilyBirthdays::isFamilyBirthday);

if (isFamilyVacation.booleanValue() || isFamilyBirthday.booleanValue())
    System.out.printf("%s is an important date!%n", date);
else
    System.out.printf("%s is not an important date.%n", date);

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