The Java Tutorials have been written for JDK 8.Java教程是为JDK 8编写的。Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.本页中描述的示例和实践没有利用后续版本中引入的改进，并且可能使用不再可用的技术。See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.有关Java SE 9及其后续版本中更新的语言特性的摘要，请参阅Java语言更改。
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.有关所有JDK版本的新功能、增强功能以及已删除或不推荐的选项的信息，请参阅JDK发行说明。
A TemporalQuery can be used to retrieve information from a temporal-based object.
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
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);