- java.lang.Object
-
- java.lang.reflect.AccessibleObject
-
- java.lang.reflect.Field
-
- All Implemented Interfaces:
- AnnotatedElement, Member
public final class Field extends AccessibleObject implements Member
AField
provides information about, and dynamic access to, a single field of a class or an interface. The reflected field may be a class (static) field or an instance field.A
Field
permits widening conversions to occur during a get or set access operation, but throws anIllegalArgumentException
if a narrowing conversion would occur.
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Method Summary
Methods Modifier and Type Method and Description boolean
equals(Object obj)
Compares thisField
against the specified object.Object
get(Object obj)
Returns the value of the field represented by thisField
, on the specified object.<T extends Annotation>
TgetAnnotation(Class<T> annotationClass)
Returns this element's annotation for the specified type if such an annotation is present, else null.boolean
getBoolean(Object obj)
Gets the value of a static or instanceboolean
field.byte
getByte(Object obj)
Gets the value of a static or instancebyte
field.char
getChar(Object obj)
Gets the value of a static or instance field of typechar
or of another primitive type convertible to typechar
via a widening conversion.Annotation[]
getDeclaredAnnotations()
Returns all annotations that are directly present on this element.Class<?>
getDeclaringClass()
Returns theClass
object representing the class or interface that declares the field represented by thisField
object.double
getDouble(Object obj)
Gets the value of a static or instance field of typedouble
or of another primitive type convertible to typedouble
via a widening conversion.float
getFloat(Object obj)
Gets the value of a static or instance field of typefloat
or of another primitive type convertible to typefloat
via a widening conversion.Type
getGenericType()
Returns aType
object that represents the declared type for the field represented by thisField
object.int
getInt(Object obj)
Gets the value of a static or instance field of typeint
or of another primitive type convertible to typeint
via a widening conversion.long
getLong(Object obj)
Gets the value of a static or instance field of typelong
or of another primitive type convertible to typelong
via a widening conversion.int
getModifiers()
Returns the Java language modifiers for the field represented by thisField
object, as an integer.String
getName()
Returns the name of the field represented by thisField
object.short
getShort(Object obj)
Gets the value of a static or instance field of typeshort
or of another primitive type convertible to typeshort
via a widening conversion.Class<?>
getType()
Returns aClass
object that identifies the declared type for the field represented by thisField
object.int
hashCode()
Returns a hashcode for thisField
.boolean
isEnumConstant()
Returnstrue
if this field represents an element of an enumerated type; returnsfalse
otherwise.boolean
isSynthetic()
Returnstrue
if this field is a synthetic field; returnsfalse
otherwise.void
set(Object obj, Object value)
Sets the field represented by thisField
object on the specified object argument to the specified new value.void
setBoolean(Object obj, boolean z)
Sets the value of a field as aboolean
on the specified object.void
setByte(Object obj, byte b)
Sets the value of a field as abyte
on the specified object.void
setChar(Object obj, char c)
Sets the value of a field as achar
on the specified object.void
setDouble(Object obj, double d)
Sets the value of a field as adouble
on the specified object.void
setFloat(Object obj, float f)
Sets the value of a field as afloat
on the specified object.void
setInt(Object obj, int i)
Sets the value of a field as anint
on the specified object.void
setLong(Object obj, long l)
Sets the value of a field as along
on the specified object.void
setShort(Object obj, short s)
Sets the value of a field as ashort
on the specified object.String
toGenericString()
Returns a string describing thisField
, including its generic type.String
toString()
Returns a string describing thisField
.-
Methods inherited from class java.lang.reflect.AccessibleObject
getAnnotations, isAccessible, isAnnotationPresent, setAccessible, setAccessible
-
-
-
-
Method Detail
-
getDeclaringClass
public Class<?> getDeclaringClass()
Returns theClass
object representing the class or interface that declares the field represented by thisField
object.- Specified by:
getDeclaringClass
in interfaceMember
- Returns:
- an object representing the declaring class of the underlying member
-
getName
public String getName()
Returns the name of the field represented by thisField
object.
-
getModifiers
public int getModifiers()
Returns the Java language modifiers for the field represented by thisField
object, as an integer. TheModifier
class should be used to decode the modifiers.- Specified by:
getModifiers
in interfaceMember
- Returns:
- the Java language modifiers for the underlying member
- See Also:
Modifier
-
isEnumConstant
public boolean isEnumConstant()
Returnstrue
if this field represents an element of an enumerated type; returnsfalse
otherwise.- Returns:
true
if and only if this field represents an element of an enumerated type.- Since:
- 1.5
-
isSynthetic
public boolean isSynthetic()
Returnstrue
if this field is a synthetic field; returnsfalse
otherwise.- Specified by:
isSynthetic
in interfaceMember
- Returns:
- true if and only if this field is a synthetic field as defined by the Java Language Specification.
- Since:
- 1.5
-
getType
public Class<?> getType()
Returns aClass
object that identifies the declared type for the field represented by thisField
object.- Returns:
- a
Class
object identifying the declared type of the field represented by this object
-
getGenericType
public Type getGenericType()
Returns aType
object that represents the declared type for the field represented by thisField
object.If the
Type
is a parameterized type, theType
object returned must accurately reflect the actual type parameters used in the source code.If the type of the underlying field is a type variable or a parameterized type, it is created. Otherwise, it is resolved.
- Returns:
- a
Type
object that represents the declared type for the field represented by thisField
object - Throws:
GenericSignatureFormatError
- if the generic field signature does not conform to the format specified in The Java™ Virtual Machine SpecificationTypeNotPresentException
- if the generic type signature of the underlying field refers to a non-existent type declarationMalformedParameterizedTypeException
- if the generic signature of the underlying field refers to a parameterized type that cannot be instantiated for any reason- Since:
- 1.5
-
equals
public boolean equals(Object obj)
Compares thisField
against the specified object. Returns true if the objects are the same. TwoField
objects are the same if they were declared by the same class and have the same name and type.- Overrides:
equals
in classObject
- Parameters:
obj
- the reference object with which to compare.- Returns:
true
if this object is the same as the obj argument;false
otherwise.- See Also:
Object.hashCode()
,HashMap
-
hashCode
public int hashCode()
Returns a hashcode for thisField
. This is computed as the exclusive-or of the hashcodes for the underlying field's declaring class name and its name.- Overrides:
hashCode
in classObject
- Returns:
- a hash code value for this object.
- See Also:
Object.equals(java.lang.Object)
,System.identityHashCode(java.lang.Object)
-
toString
public String toString()
Returns a string describing thisField
. The format is the access modifiers for the field, if any, followed by the field type, followed by a space, followed by the fully-qualified name of the class declaring the field, followed by a period, followed by the name of the field. For example:public static final int java.lang.Thread.MIN_PRIORITY private int java.io.FileDescriptor.fd
The modifiers are placed in canonical order as specified by "The Java Language Specification". This is
public
,protected
orprivate
first, and then other modifiers in the following order:static
,final
,transient
,volatile
.
-
toGenericString
public String toGenericString()
Returns a string describing thisField
, including its generic type. The format is the access modifiers for the field, if any, followed by the generic field type, followed by a space, followed by the fully-qualified name of the class declaring the field, followed by a period, followed by the name of the field.The modifiers are placed in canonical order as specified by "The Java Language Specification". This is
public
,protected
orprivate
first, and then other modifiers in the following order:static
,final
,transient
,volatile
.- Returns:
- a string describing this
Field
, including its generic type - Since:
- 1.5
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get
public Object get(Object obj) throws IllegalArgumentException, IllegalAccessException
Returns the value of the field represented by thisField
, on the specified object. The value is automatically wrapped in an object if it has a primitive type.The underlying field's value is obtained as follows:
If the underlying field is a static field, the
obj
argument is ignored; it may be null.Otherwise, the underlying field is an instance field. If the specified
obj
argument is null, the method throws aNullPointerException
. If the specified object is not an instance of the class or interface declaring the underlying field, the method throws anIllegalArgumentException
.If this
Field
object is enforcing Java language access control, and the underlying field is inaccessible, the method throws anIllegalAccessException
. If the underlying field is static, the class that declared the field is initialized if it has not already been initialized.Otherwise, the value is retrieved from the underlying instance or static field. If the field has a primitive type, the value is wrapped in an object before being returned, otherwise it is returned as is.
If the field is hidden in the type of
obj
, the field's value is obtained according to the preceding rules.- Parameters:
obj
- object from which the represented field's value is to be extracted- Returns:
- the value of the represented field in object
obj
; primitive values are wrapped in an appropriate object before being returned - Throws:
IllegalAccessException
- if thisField
object is enforcing Java language access control and the underlying field is inaccessible.IllegalArgumentException
- if the specified object is not an instance of the class or interface declaring the underlying field (or a subclass or implementor thereof).NullPointerException
- if the specified object is null and the field is an instance field.ExceptionInInitializerError
- if the initialization provoked by this method fails.
-
getBoolean
public boolean getBoolean(Object obj) throws IllegalArgumentException, IllegalAccessException
Gets the value of a static or instanceboolean
field.- Parameters:
obj
- the object to extract theboolean
value from- Returns:
- the value of the
boolean
field - Throws:
IllegalAccessException
- if thisField
object is enforcing Java language access control and the underlying field is inaccessible.IllegalArgumentException
- if the specified object is not an instance of the class or interface declaring the underlying field (or a subclass or implementor thereof), or if the field value cannot be converted to the typeboolean
by a widening conversion.NullPointerException
- if the specified object is null and the field is an instance field.ExceptionInInitializerError
- if the initialization provoked by this method fails.- See Also:
get(java.lang.Object)
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getByte
public byte getByte(Object obj) throws IllegalArgumentException, IllegalAccessException
Gets the value of a static or instancebyte
field.- Parameters:
obj
- the object to extract thebyte
value from- Returns:
- the value of the
byte
field - Throws:
IllegalAccessException
- if thisField
object is enforcing Java language access control and the underlying field is inaccessible.IllegalArgumentException
- if the specified object is not an instance of the class or interface declaring the underlying field (or a subclass or implementor thereof), or if the field value cannot be converted to the typebyte
by a widening conversion.NullPointerException
- if the specified object is null and the field is an instance field.ExceptionInInitializerError
- if the initialization provoked by this method fails.- See Also:
get(java.lang.Object)
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getChar
public char getChar(Object obj) throws IllegalArgumentException, IllegalAccessException
Gets the value of a static or instance field of typechar
or of another primitive type convertible to typechar
via a widening conversion.- Parameters:
obj
- the object to extract thechar
value from- Returns:
- the value of the field converted to type
char
- Throws:
IllegalAccessException
- if thisField
object is enforcing Java language access control and the underlying field is inaccessible.IllegalArgumentException
- if the specified object is not an instance of the class or interface declaring the underlying field (or a subclass or implementor thereof), or if the field value cannot be converted to the typechar
by a widening conversion.NullPointerException
- if the specified object is null and the field is an instance field.ExceptionInInitializerError
- if the initialization provoked by this method fails.- See Also:
get(java.lang.Object)
-
getShort
public short getShort(Object obj) throws IllegalArgumentException, IllegalAccessException
Gets the value of a static or instance field of typeshort
or of another primitive type convertible to typeshort
via a widening conversion.- Parameters:
obj
- the object to extract theshort
value from- Returns:
- the value of the field converted to type
short
- Throws:
IllegalAccessException
- if thisField
object is enforcing Java language access control and the underlying field is inaccessible.IllegalArgumentException
- if the specified object is not an instance of the class or interface declaring the underlying field (or a subclass or implementor thereof), or if the field value cannot be converted to the typeshort
by a widening conversion.NullPointerException
- if the specified object is null and the field is an instance field.ExceptionInInitializerError
- if the initialization provoked by this method fails.- See Also:
get(java.lang.Object)
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getInt
public int getInt(Object obj) throws IllegalArgumentException, IllegalAccessException
Gets the value of a static or instance field of typeint
or of another primitive type convertible to typeint
via a widening conversion.- Parameters:
obj
- the object to extract theint
value from- Returns:
- the value of the field converted to type
int
- Throws:
IllegalAccessException
- if thisField
object is enforcing Java language access control and the underlying field is inaccessible.IllegalArgumentException
- if the specified object is not an instance of the class or interface declaring the underlying field (or a subclass or implementor thereof), or if the field value cannot be converted to the typeint
by a widening conversion.NullPointerException
- if the specified object is null and the field is an instance field.ExceptionInInitializerError
- if the initialization provoked by this method fails.- See Also:
get(java.lang.Object)
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getLong
public long getLong(Object obj) throws IllegalArgumentException, IllegalAccessException
Gets the value of a static or instance field of typelong
or of another primitive type convertible to typelong
via a widening conversion.- Parameters:
obj
- the object to extract thelong
value from- Returns:
- the value of the field converted to type
long
- Throws:
IllegalAccessException
- if thisField
object is enforcing Java language access control and the underlying field is inaccessible.IllegalArgumentException
- if the specified object is not an instance of the class or interface declaring the underlying field (or a subclass or implementor thereof), or if the field value cannot be converted to the typelong
by a widening conversion.NullPointerException
- if the specified object is null and the field is an instance field.ExceptionInInitializerError
- if the initialization provoked by this method fails.- See Also:
get(java.lang.Object)
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getFloat
public float getFloat(Object obj) throws IllegalArgumentException, IllegalAccessException
Gets the value of a static or instance field of typefloat
or of another primitive type convertible to typefloat
via a widening conversion.- Parameters:
obj
- the object to extract thefloat
value from- Returns:
- the value of the field converted to type
float
- Throws:
IllegalAccessException
- if thisField
object is enforcing Java language access control and the underlying field is inaccessible.IllegalArgumentException
- if the specified object is not an instance of the class or interface declaring the underlying field (or a subclass or implementor thereof), or if the field value cannot be converted to the typefloat
by a widening conversion.NullPointerException
- if the specified object is null and the field is an instance field.ExceptionInInitializerError
- if the initialization provoked by this method fails.- See Also:
get(java.lang.Object)
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getDouble
public double getDouble(Object obj) throws IllegalArgumentException, IllegalAccessException
Gets the value of a static or instance field of typedouble
or of another primitive type convertible to typedouble
via a widening conversion.- Parameters:
obj
- the object to extract thedouble
value from- Returns:
- the value of the field converted to type
double
- Throws:
IllegalAccessException
- if thisField
object is enforcing Java language access control and the underlying field is inaccessible.IllegalArgumentException
- if the specified object is not an instance of the class or interface declaring the underlying field (or a subclass or implementor thereof), or if the field value cannot be converted to the typedouble
by a widening conversion.NullPointerException
- if the specified object is null and the field is an instance field.ExceptionInInitializerError
- if the initialization provoked by this method fails.- See Also:
get(java.lang.Object)
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set
public void set(Object obj, Object value) throws IllegalArgumentException, IllegalAccessException
Sets the field represented by thisField
object on the specified object argument to the specified new value. The new value is automatically unwrapped if the underlying field has a primitive type.The operation proceeds as follows:
If the underlying field is static, the
obj
argument is ignored; it may be null.Otherwise the underlying field is an instance field. If the specified object argument is null, the method throws a
NullPointerException
. If the specified object argument is not an instance of the class or interface declaring the underlying field, the method throws anIllegalArgumentException
.If this
Field
object is enforcing Java language access control, and the underlying field is inaccessible, the method throws anIllegalAccessException
.If the underlying field is final, the method throws an
IllegalAccessException
unlesssetAccessible(true)
has succeeded for thisField
object and the field is non-static. Setting a final field in this way is meaningful only during deserialization or reconstruction of instances of classes with blank final fields, before they are made available for access by other parts of a program. Use in any other context may have unpredictable effects, including cases in which other parts of a program continue to use the original value of this field.If the underlying field is of a primitive type, an unwrapping conversion is attempted to convert the new value to a value of a primitive type. If this attempt fails, the method throws an
IllegalArgumentException
.If, after possible unwrapping, the new value cannot be converted to the type of the underlying field by an identity or widening conversion, the method throws an
IllegalArgumentException
.If the underlying field is static, the class that declared the field is initialized if it has not already been initialized.
The field is set to the possibly unwrapped and widened new value.
If the field is hidden in the type of
obj
, the field's value is set according to the preceding rules.- Parameters:
obj
- the object whose field should be modifiedvalue
- the new value for the field ofobj
being modified- Throws:
IllegalAccessException
- if thisField
object is enforcing Java language access control and the underlying field is either inaccessible or final.IllegalArgumentException
- if the specified object is not an instance of the class or interface declaring the underlying field (or a subclass or implementor thereof), or if an unwrapping conversion fails.NullPointerException
- if the specified object is null and the field is an instance field.ExceptionInInitializerError
- if the initialization provoked by this method fails.
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setBoolean
public void setBoolean(Object obj, boolean z) throws IllegalArgumentException, IllegalAccessException
Sets the value of a field as aboolean
on the specified object. This method is equivalent toset(obj, zObj)
, wherezObj
is aBoolean
object andzObj.booleanValue() == z
.- Parameters:
obj
- the object whose field should be modifiedz
- the new value for the field ofobj
being modified- Throws:
IllegalAccessException
- if thisField
object is enforcing Java language access control and the underlying field is either inaccessible or final.IllegalArgumentException
- if the specified object is not an instance of the class or interface declaring the underlying field (or a subclass or implementor thereof), or if an unwrapping conversion fails.NullPointerException
- if the specified object is null and the field is an instance field.ExceptionInInitializerError
- if the initialization provoked by this method fails.- See Also:
set(java.lang.Object, java.lang.Object)
-
setByte
public void setByte(Object obj, byte b) throws IllegalArgumentException, IllegalAccessException
Sets the value of a field as abyte
on the specified object. This method is equivalent toset(obj, bObj)
, wherebObj
is aByte
object andbObj.byteValue() == b
.- Parameters:
obj
- the object whose field should be modifiedb
- the new value for the field ofobj
being modified- Throws:
IllegalAccessException
- if thisField
object is enforcing Java language access control and the underlying field is either inaccessible or final.IllegalArgumentException
- if the specified object is not an instance of the class or interface declaring the underlying field (or a subclass or implementor thereof), or if an unwrapping conversion fails.NullPointerException
- if the specified object is null and the field is an instance field.ExceptionInInitializerError
- if the initialization provoked by this method fails.- See Also:
set(java.lang.Object, java.lang.Object)
-
setChar
public void setChar(Object obj, char c) throws IllegalArgumentException, IllegalAccessException
Sets the value of a field as achar
on the specified object. This method is equivalent toset(obj, cObj)
, wherecObj
is aCharacter
object andcObj.charValue() == c
.- Parameters:
obj
- the object whose field should be modifiedc
- the new value for the field ofobj
being modified- Throws:
IllegalAccessException
- if thisField
object is enforcing Java language access control and the underlying field is either inaccessible or final.IllegalArgumentException
- if the specified object is not an instance of the class or interface declaring the underlying field (or a subclass or implementor thereof), or if an unwrapping conversion fails.NullPointerException
- if the specified object is null and the field is an instance field.ExceptionInInitializerError
- if the initialization provoked by this method fails.- See Also:
set(java.lang.Object, java.lang.Object)
-
setShort
public void setShort(Object obj, short s) throws IllegalArgumentException, IllegalAccessException
Sets the value of a field as ashort
on the specified object. This method is equivalent toset(obj, sObj)
, wheresObj
is aShort
object andsObj.shortValue() == s
.- Parameters:
obj
- the object whose field should be modifieds
- the new value for the field ofobj
being modified- Throws:
IllegalAccessException
- if thisField
object is enforcing Java language access control and the underlying field is either inaccessible or final.IllegalArgumentException
- if the specified object is not an instance of the class or interface declaring the underlying field (or a subclass or implementor thereof), or if an unwrapping conversion fails.NullPointerException
- if the specified object is null and the field is an instance field.ExceptionInInitializerError
- if the initialization provoked by this method fails.- See Also:
set(java.lang.Object, java.lang.Object)
-
setInt
public void setInt(Object obj, int i) throws IllegalArgumentException, IllegalAccessException
Sets the value of a field as anint
on the specified object. This method is equivalent toset(obj, iObj)
, whereiObj
is aInteger
object andiObj.intValue() == i
.- Parameters:
obj
- the object whose field should be modifiedi
- the new value for the field ofobj
being modified- Throws:
IllegalAccessException
- if thisField
object is enforcing Java language access control and the underlying field is either inaccessible or final.IllegalArgumentException
- if the specified object is not an instance of the class or interface declaring the underlying field (or a subclass or implementor thereof), or if an unwrapping conversion fails.NullPointerException
- if the specified object is null and the field is an instance field.ExceptionInInitializerError
- if the initialization provoked by this method fails.- See Also:
set(java.lang.Object, java.lang.Object)
-
setLong
public void setLong(Object obj, long l) throws IllegalArgumentException, IllegalAccessException
Sets the value of a field as along
on the specified object. This method is equivalent toset(obj, lObj)
, wherelObj
is aLong
object andlObj.longValue() == l
.- Parameters:
obj
- the object whose field should be modifiedl
- the new value for the field ofobj
being modified- Throws:
IllegalAccessException
- if thisField
object is enforcing Java language access control and the underlying field is either inaccessible or final.IllegalArgumentException
- if the specified object is not an instance of the class or interface declaring the underlying field (or a subclass or implementor thereof), or if an unwrapping conversion fails.NullPointerException
- if the specified object is null and the field is an instance field.ExceptionInInitializerError
- if the initialization provoked by this method fails.- See Also:
set(java.lang.Object, java.lang.Object)
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setFloat
public void setFloat(Object obj, float f) throws IllegalArgumentException, IllegalAccessException
Sets the value of a field as afloat
on the specified object. This method is equivalent toset(obj, fObj)
, wherefObj
is aFloat
object andfObj.floatValue() == f
.- Parameters:
obj
- the object whose field should be modifiedf
- the new value for the field ofobj
being modified- Throws:
IllegalAccessException
- if thisField
object is enforcing Java language access control and the underlying field is either inaccessible or final.IllegalArgumentException
- if the specified object is not an instance of the class or interface declaring the underlying field (or a subclass or implementor thereof), or if an unwrapping conversion fails.NullPointerException
- if the specified object is null and the field is an instance field.ExceptionInInitializerError
- if the initialization provoked by this method fails.- See Also:
set(java.lang.Object, java.lang.Object)
-
setDouble
public void setDouble(Object obj, double d) throws IllegalArgumentException, IllegalAccessException
Sets the value of a field as adouble
on the specified object. This method is equivalent toset(obj, dObj)
, wheredObj
is aDouble
object anddObj.doubleValue() == d
.- Parameters:
obj
- the object whose field should be modifiedd
- the new value for the field ofobj
being modified- Throws:
IllegalAccessException
- if thisField
object is enforcing Java language access control and the underlying field is either inaccessible or final.IllegalArgumentException
- if the specified object is not an instance of the class or interface declaring the underlying field (or a subclass or implementor thereof), or if an unwrapping conversion fails.NullPointerException
- if the specified object is null and the field is an instance field.ExceptionInInitializerError
- if the initialization provoked by this method fails.- See Also:
set(java.lang.Object, java.lang.Object)
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getAnnotation
public <T extends Annotation> T getAnnotation(Class<T> annotationClass)
Description copied from interface:AnnotatedElement
Returns this element's annotation for the specified type if such an annotation is present, else null.- Specified by:
getAnnotation
in interfaceAnnotatedElement
- Overrides:
getAnnotation
in classAccessibleObject
- Parameters:
annotationClass
- the Class object corresponding to the annotation type- Returns:
- this element's annotation for the specified annotation type if present on this element, else null
- Throws:
NullPointerException
- if the given annotation class is null- Since:
- 1.5
-
getDeclaredAnnotations
public Annotation[] getDeclaredAnnotations()
Description copied from interface:AnnotatedElement
Returns all annotations that are directly present on this element. Unlike the other methods in this interface, this method ignores inherited annotations. (Returns an array of length zero if no annotations are directly present on this element.) The caller of this method is free to modify the returned array; it will have no effect on the arrays returned to other callers.- Specified by:
getDeclaredAnnotations
in interfaceAnnotatedElement
- Overrides:
getDeclaredAnnotations
in classAccessibleObject
- Returns:
- All annotations directly present on this element
- Since:
- 1.5
-
-
Document created the 11/06/2005, last modified the 04/03/2020
Source of the printed document:https://www.gaudry.be/en/java-api-rf-java/lang/reflect/field.html
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