[Java] Annotation Type Lazy
- groovy.lang.Lazy
Field annotation to simplify lazy initialization.
Example usage without any special modifiers just defers initialization until the first call but is not thread-safe:
@Lazy
T x
becomes private T $x T getX() { if ($x != null) return $x else { $x = new T() return $x } }If the field is declared volatile then initialization will be synchronized using the double-checked locking pattern as shown here:
@Lazy
volatile T x
becomes private volatile T $x T getX() { T $x_local = $x if ($x_local != null) return $x_local else { synchronized(this) { if ($x == null) { $x = new T() } return $x } } }By default a field will be initialized by calling its default constructor. If the field has an initial value expression then this expression will be used instead of calling the default constructor. In particular, it is possible to use closure
{ ... } ()
syntax as follows:
@Lazy
T x = { [1, 2, 3] } ()
becomes private T $x T getX() { T $x_local = $x if ($x_local != null) return $x_local else { synchronized(this) { if ($x == null) { $x = { [1, 2, 3] } () } return $x } } }
@Lazy(soft=true)
will use a soft reference instead of the field and use the above rules each time re-initialization is required.
If the soft
flag for the annotation is not set but the field is static, then the initialization on demand holder idiom is used as follows:
becomes these methods and inners classes within the class containing the above definitions:@Lazy
static FieldType field@Lazy
static Date date1@Lazy
static Date date2 = { new Date().copyWith(year: 2000) }()@Lazy
static Date date3 = new GregorianCalendar(2009, Calendar.JANUARY, 1).time
private static class FieldTypeHolder_field { private static final FieldType INSTANCE = new FieldType() } private static class DateHolder_date1 { private static final Date INSTANCE = new Date() } private static class DateHolder_date2 { private static final Date INSTANCE = { new Date().copyWith(year: 2000) }() } private static class DateHolder_date3 { private static final Date INSTANCE = new GregorianCalendar(2009, Calendar.JANUARY, 1).time } static FieldType getField() { return FieldTypeHolder_field.INSTANCE } static Date getDate1() { return DateHolder_date1.INSTANCE } static Date getDate2() { return DateHolder_date2.INSTANCE } static Date getDate3() { return DateHolder_date3.INSTANCE }
Element Summary
Type | Name and Description |
---|---|
boolean |
soft @default false
|
Inherited Methods Summary
Methods inherited from class | Name |
---|---|
class Object | wait, wait, wait, equals, toString, hashCode, getClass, notify, notifyAll |
Element Detail
public boolean soft
@default false
- Returns:
- if field should be soft referenced instead of hard referenced
© 2003-2020 The Apache Software Foundation
Licensed under the Apache license.
https://docs.groovy-lang.org/2.5.14/html/gapi/groovy/lang/Lazy.html