Field
public
final
class
Field
extends AccessibleObject
implements
Member
java.lang.Object | ||
↳ | java.lang.reflect.AccessibleObject | |
↳ | java.lang.reflect.Field |
A Field
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 an IllegalArgumentException
if a
narrowing conversion would occur.
See also:
Summary
Inherited constants |
---|
Public methods | |
---|---|
boolean
|
equals(Object obj)
Compares this |
Object
|
get(Object obj)
Returns the value of the field represented by this |
<T extends Annotation>
T
|
getAnnotation(Class<T> annotationClass)
Returns this element's annotation for the specified type if such an annotation is present, else null. |
<T extends Annotation>
T[]
|
getAnnotationsByType(Class<T> annotationClass)
Returns annotations that are associated with this element. |
boolean
|
getBoolean(Object obj)
Gets the value of a static or instance |
byte
|
getByte(Object obj)
Gets the value of a static or instance |
char
|
getChar(Object obj)
Gets the value of a static or instance field of type
|
Annotation[]
|
getDeclaredAnnotations()
Returns annotations that are directly present on this element. |
Class<?>
|
getDeclaringClass()
Returns the |
double
|
getDouble(Object obj)
Gets the value of a static or instance field of type
|
float
|
getFloat(Object obj)
Gets the value of a static or instance field of type
|
Type
|
getGenericType()
Returns a |
int
|
getInt(Object obj)
Gets the value of a static or instance field of type
|
long
|
getLong(Object obj)
Gets the value of a static or instance field of type
|
int
|
getModifiers()
Returns the Java language modifiers for the field represented
by this |
String
|
getName()
Returns the name of the field represented by this |
short
|
getShort(Object obj)
Gets the value of a static or instance field of type
|
Class<?>
|
getType()
Returns a |
int
|
hashCode()
Returns a hashcode for this |
boolean
|
isAnnotationPresent(Class<? extends Annotation> annotationType)
Returns true if an annotation for the specified type is present on this element, else false. |
boolean
|
isEnumConstant()
Returns |
boolean
|
isSynthetic()
Returns |
void
|
set(Object obj, Object value)
Sets the field represented by this |
void
|
setBoolean(Object obj, boolean z)
Sets the value of a field as a |
void
|
setByte(Object obj, byte b)
Sets the value of a field as a |
void
|
setChar(Object obj, char c)
Sets the value of a field as a |
void
|
setDouble(Object obj, double d)
Sets the value of a field as a |
void
|
setFloat(Object obj, float f)
Sets the value of a field as a |
void
|
setInt(Object obj, int i)
Sets the value of a field as an |
void
|
setLong(Object obj, long l)
Sets the value of a field as a |
void
|
setShort(Object obj, short s)
Sets the value of a field as a |
String
|
toGenericString()
Returns a string describing this |
String
|
toString()
Returns a string describing this |
Inherited methods | |
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Public methods
equals
public boolean equals (Object obj)
Compares this Field
against the specified object. Returns
true if the objects are the same. Two Field
objects are the same if
they were declared by the same class and have the same name
and type.
Parameters | |
---|---|
obj |
Object : the reference object with which to compare. |
Returns | |
---|---|
boolean |
true if this object is the same as the obj
argument; false otherwise. |
get
public Object get (Object obj)
Returns the value of the field represented by this Field
, 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 a
NullPointerException
. If the specified object is not an
instance of the class or interface declaring the underlying
field, the method throws an IllegalArgumentException
.
If this Field
object is enforcing Java language access control, and
the underlying field is inaccessible, the method throws an
IllegalAccessException
.
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 : object from which the represented field's value is
to be extracted |
Returns | |
---|---|
Object |
the value of the represented field in object
obj ; primitive values are wrapped in an appropriate
object before being returned |
Throws | |
---|---|
IllegalAccessException |
if this Field 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. |
getAnnotation
public T getAnnotation (Class<T> annotationClass)
Returns this element's annotation for the specified type if such an annotation is present, else null.
Parameters | |
---|---|
annotationClass |
Class : the Class object corresponding to the
annotation type |
Returns | |
---|---|
T |
this element's annotation for the specified annotation type if present on this element, else null |
Throws | |
---|---|
NullPointerException |
getAnnotationsByType
public T[] getAnnotationsByType (Class<T> annotationClass)
Returns annotations that are associated with this element.
If there are no annotations associated with this element, the return
value is an array of length 0.
The difference between this method and getAnnotation(java.lang.Class)
is that this method detects if its argument is a repeatable
annotation type (JLS 9.6), and if so, attempts to find one or
more annotations of that type by "looking through" a container
annotation.
The caller of this method is free to modify the returned array; it will
have no effect on the arrays returned to other callers.
Parameters | |
---|---|
annotationClass |
Class : the Class object corresponding to the
annotation type |
Returns | |
---|---|
T[] |
all this element's annotations for the specified annotation type if associated with this element, else an array of length zero |
Throws | |
---|---|
NullPointerException |
getBoolean
public boolean getBoolean (Object obj)
Gets the value of a static or instance boolean
field.
Parameters | |
---|---|
obj |
Object : the object to extract the boolean value
from |
Returns | |
---|---|
boolean |
the value of the boolean field |
Throws | |
---|---|
IllegalAccessException |
if this Field 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 type boolean 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:
getByte
public byte getByte (Object obj)
Gets the value of a static or instance byte
field.
Parameters | |
---|---|
obj |
Object : the object to extract the byte value
from |
Returns | |
---|---|
byte |
the value of the byte field |
Throws | |
---|---|
IllegalAccessException |
if this Field 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 type byte 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:
getChar
public char getChar (Object obj)
Gets the value of a static or instance field of type
char
or of another primitive type convertible to
type char
via a widening conversion.
Parameters | |
---|---|
obj |
Object : the object to extract the char value
from |
Returns | |
---|---|
char |
the value of the field converted to type char |
Throws | |
---|---|
IllegalAccessException |
if this Field 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 type char 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:
getDeclaredAnnotations
public Annotation[] getDeclaredAnnotations ()
Returns annotations that are directly present on this element. This method ignores inherited annotations. If there are no annotations directly present on this element, the return value is an array of length 0. The caller of this method is free to modify the returned array; it will have no effect on the arrays returned to other callers.
Returns | |
---|---|
Annotation[] |
annotations directly present on this element |
getDeclaringClass
public Class<?> getDeclaringClass ()
Returns the Class
object representing the class or interface
that declares the field represented by this Field
object.
Returns | |
---|---|
Class<?> |
an object representing the declaring class of the underlying member |
getDouble
public double getDouble (Object obj)
Gets the value of a static or instance field of type
double
or of another primitive type convertible to
type double
via a widening conversion.
Parameters | |
---|---|
obj |
Object : the object to extract the double value
from |
Returns | |
---|---|
double |
the value of the field converted to type double |
Throws | |
---|---|
IllegalAccessException |
if this Field 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 type double 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:
getFloat
public float getFloat (Object obj)
Gets the value of a static or instance field of type
float
or of another primitive type convertible to
type float
via a widening conversion.
Parameters | |
---|---|
obj |
Object : the object to extract the float value
from |
Returns | |
---|---|
float |
the value of the field converted to type float |
Throws | |
---|---|
IllegalAccessException |
if this Field 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 type float 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:
getGenericType
public Type getGenericType ()
Returns a Type
object that represents the declared type for
the field represented by this Field
object.
If the Type
is a parameterized type, the
Type
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 | |
---|---|
Type |
a Type object that represents the declared type for
the field represented by this Field object |
Throws | |
---|---|
GenericSignatureFormatError |
if the generic field signature does not conform to the format specified in The Java™ Virtual Machine Specification |
TypeNotPresentException |
if the generic type signature of the underlying field refers to a non-existent type declaration |
MalformedParameterizedTypeException |
if the generic signature of the underlying field refers to a parameterized type that cannot be instantiated for any reason |
getInt
public int getInt (Object obj)
Gets the value of a static or instance field of type
int
or of another primitive type convertible to
type int
via a widening conversion.
Parameters | |
---|---|
obj |
Object : the object to extract the int value
from |
Returns | |
---|---|
int |
the value of the field converted to type int |
Throws | |
---|---|
IllegalAccessException |
if this Field 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 type int 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:
getLong
public long getLong (Object obj)
Gets the value of a static or instance field of type
long
or of another primitive type convertible to
type long
via a widening conversion.
Parameters | |
---|---|
obj |
Object : the object to extract the long value
from |
Returns | |
---|---|
long |
the value of the field converted to type long |
Throws | |
---|---|
IllegalAccessException |
if this Field 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 type long 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:
getModifiers
public int getModifiers ()
Returns the Java language modifiers for the field represented
by this Field
object, as an integer. The Modifier
class should
be used to decode the modifiers.
Returns | |
---|---|
int |
the Java language modifiers for the underlying member |
See also:
getName
public String getName ()
Returns the name of the field represented by this Field
object.
Returns | |
---|---|
String |
the simple name of the underlying member |
getShort
public short getShort (Object obj)
Gets the value of a static or instance field of type
short
or of another primitive type convertible to
type short
via a widening conversion.
Parameters | |
---|---|
obj |
Object : the object to extract the short value
from |
Returns | |
---|---|
short |
the value of the field converted to type short |
Throws | |
---|---|
IllegalAccessException |
if this Field 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 type short 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:
getType
public Class<?> getType ()
Returns a Class
object that identifies the
declared type for the field represented by this
Field
object.
Returns | |
---|---|
Class<?> |
a Class object identifying the declared
type of the field represented by this object |
hashCode
public int hashCode ()
Returns a hashcode for this Field
. This is computed as the
exclusive-or of the hashcodes for the underlying field's
declaring class name and its name.
Returns | |
---|---|
int |
a hash code value for this object. |
isAnnotationPresent
public boolean isAnnotationPresent (Class<? extends Annotation> annotationType)
Returns true if an annotation for the specified type is present on this element, else false. This method is designed primarily for convenient access to marker annotations.
The truth value returned by this method is equivalent to:
getAnnotation(annotationClass) != null
The body of the default method is specified to be the code above.
Parameters | |
---|---|
annotationType |
Class : the Class object corresponding to the
annotation type |
Returns | |
---|---|
boolean |
true if an annotation for the specified annotation type is present on this element, else false |
isEnumConstant
public boolean isEnumConstant ()
Returns true
if this field represents an element of
an enumerated type; returns false
otherwise.
Returns | |
---|---|
boolean |
true if and only if this field represents an element of
an enumerated type. |
isSynthetic
public boolean isSynthetic ()
Returns true
if this field is a synthetic
field; returns false
otherwise.
Returns | |
---|---|
boolean |
true if and only if this field is a synthetic field as defined by the Java Language Specification. |
set
public void set (Object obj, Object value)
Sets the field represented by this Field
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 an IllegalArgumentException
.
If this Field
object is enforcing Java language access control, and
the underlying field is inaccessible, the method throws an
IllegalAccessException
.
If the underlying field is final, this Field
object has
write access if and only if the following conditions are met:
setAccessible(true)
has succeeded for thisField
object;- the field is non-static; and
- the field's declaring class is not a record class.
IllegalAccessException
.
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 |
Object : the object whose field should be modified |
value |
Object : the new value for the field of obj
being modified |
Throws | |
---|---|
IllegalAccessException |
if this Field 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. |
setBoolean
public void setBoolean (Object obj, boolean z)
Sets the value of a field as a boolean
on the specified object.
This method is equivalent to
set(obj, zObj)
,
where zObj
is a Boolean
object and
zObj.booleanValue() == z
.
Parameters | |
---|---|
obj |
Object : the object whose field should be modified |
z |
boolean : the new value for the field of obj
being modified |
Throws | |
---|---|
IllegalAccessException |
if this Field 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:
setByte
public void setByte (Object obj, byte b)
Sets the value of a field as a byte
on the specified object.
This method is equivalent to
set(obj, bObj)
,
where bObj
is a Byte
object and
bObj.byteValue() == b
.
Parameters | |
---|---|
obj |
Object : the object whose field should be modified |
b |
byte : the new value for the field of obj
being modified |
Throws | |
---|---|
IllegalAccessException |
if this Field 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:
setChar
public void setChar (Object obj, char c)
Sets the value of a field as a char
on the specified object.
This method is equivalent to
set(obj, cObj)
,
where cObj
is a Character
object and
cObj.charValue() == c
.
Parameters | |
---|---|
obj |
Object : the object whose field should be modified |
c |
char : the new value for the field of obj
being modified |
Throws | |
---|---|
IllegalAccessException |
if this Field 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:
setDouble
public void setDouble (Object obj, double d)
Sets the value of a field as a double
on the specified object.
This method is equivalent to
set(obj, dObj)
,
where dObj
is a Double
object and
dObj.doubleValue() == d
.
Parameters | |
---|---|
obj |
Object : the object whose field should be modified |
d |
double : the new value for the field of obj
being modified |
Throws | |
---|---|
IllegalAccessException |
if this Field 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:
setFloat
public void setFloat (Object obj, float f)
Sets the value of a field as a float
on the specified object.
This method is equivalent to
set(obj, fObj)
,
where fObj
is a Float
object and
fObj.floatValue() == f
.
Parameters | |
---|---|
obj |
Object : the object whose field should be modified |
f |
float : the new value for the field of obj
being modified |
Throws | |
---|---|
IllegalAccessException |
if this Field 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:
setInt
public void setInt (Object obj, int i)
Sets the value of a field as an int
on the specified object.
This method is equivalent to
set(obj, iObj)
,
where iObj
is a Integer
object and
iObj.intValue() == i
.
Parameters | |
---|---|
obj |
Object : the object whose field should be modified |
i |
int : the new value for the field of obj
being modified |
Throws | |
---|---|
IllegalAccessException |
if this Field 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:
setLong
public void setLong (Object obj, long l)
Sets the value of a field as a long
on the specified object.
This method is equivalent to
set(obj, lObj)
,
where lObj
is a Long
object and
lObj.longValue() == l
.
Parameters | |
---|---|
obj |
Object : the object whose field should be modified |
l |
long : the new value for the field of obj
being modified |
Throws | |
---|---|
IllegalAccessException |
if this Field 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:
setShort
public void setShort (Object obj, short s)
Sets the value of a field as a short
on the specified object.
This method is equivalent to
set(obj, sObj)
,
where sObj
is a Short
object and
sObj.shortValue() == s
.
Parameters | |
---|---|
obj |
Object : the object whose field should be modified |
s |
short : the new value for the field of obj
being modified |
Throws | |
---|---|
IllegalAccessException |
if this Field 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:
toGenericString
public String toGenericString ()
Returns a string describing this Field
, 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
or private
first, and then other
modifiers in the following order: static
, final
,
transient
, volatile
.
Returns | |
---|---|
String |
a string describing this Field , including
its generic type |
toString
public String toString ()
Returns a string describing this Field
. 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
or private
first, and then other
modifiers in the following order: static
, final
,
transient
, volatile
.
Returns | |
---|---|
String |
a string describing this Field |