public final class Field extends AccessibleObject implements Member
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.
Member
, Class
, Class.getFields()
, Class.getField(String)
, Class.getDeclaredFields()
, Class.getDeclaredField(String)
DECLARED, PUBLIC
public Class<?> getDeclaringClass()
Returns the Class
object representing the class or interface that declares the field represented by this Field
object.
getDeclaringClass
in interface Member
public String getName()
Returns the name of the field represented by this Field
object.
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.
getModifiers
in interface Member
Modifier
public boolean isEnumConstant()
Returns true
if this field represents an element of an enumerated type; returns false
otherwise.
true
if and only if this field represents an element of an enumerated type.public boolean isSynthetic()
Returns true
if this field is a synthetic field; returns false
otherwise.
isSynthetic
in interface Member
public Class<?> getType()
Returns a Class
object that identifies the declared type for the field represented by this Field
object.
Class
object identifying the declared type of the field represented by this objectpublic 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.
Type
object that represents the declared type for the field represented by this Field
objectGenericSignatureFormatError
- 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 declarationMalformedParameterizedTypeException
- if the generic signature of the underlying field refers to a parameterized type that cannot be instantiated for any reasonpublic 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.
equals
in class Object
obj
- the reference object with which to compare.true
if this object is the same as the obj argument; false
otherwise.Object.hashCode()
, HashMap
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.
hashCode
in class Object
Object.equals(java.lang.Object)
, System.identityHashCode(java.lang.Object)
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
.
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
.
Field
, including its generic typepublic Object get(Object obj) throws IllegalArgumentException, IllegalAccessException
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.
obj
- object from which the represented field's value is to be extractedobj
; primitive values are wrapped in an appropriate object before being returnedIllegalAccessException
- 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.public boolean getBoolean(Object obj) throws IllegalArgumentException, IllegalAccessException
Gets the value of a static or instance boolean
field.
obj
- the object to extract the boolean
value fromboolean
fieldIllegalAccessException
- 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.get(java.lang.Object)
public byte getByte(Object obj) throws IllegalArgumentException, IllegalAccessException
Gets the value of a static or instance byte
field.
obj
- the object to extract the byte
value frombyte
fieldIllegalAccessException
- 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.get(java.lang.Object)
public char getChar(Object obj) throws IllegalArgumentException, IllegalAccessException
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.
obj
- the object to extract the char
value fromchar
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.get(java.lang.Object)
public short getShort(Object obj) throws IllegalArgumentException, IllegalAccessException
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.
obj
- the object to extract the short
value fromshort
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.get(java.lang.Object)
public int getInt(Object obj) throws IllegalArgumentException, IllegalAccessException
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.
obj
- the object to extract the int
value fromint
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.get(java.lang.Object)
public long getLong(Object obj) throws IllegalArgumentException, IllegalAccessException
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.
obj
- the object to extract the long
value fromlong
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.get(java.lang.Object)
public float getFloat(Object obj) throws IllegalArgumentException, IllegalAccessException
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.
obj
- the object to extract the float
value fromfloat
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.get(java.lang.Object)
public double getDouble(Object obj) throws IllegalArgumentException, IllegalAccessException
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.
obj
- the object to extract the double
value fromdouble
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.get(java.lang.Object)
public void set(Object obj, Object value) throws IllegalArgumentException, IllegalAccessException
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, the method throws an IllegalAccessException
unless setAccessible(true)
has succeeded for this Field
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.
obj
- the object whose field should be modifiedvalue
- the new value for the field of obj
being modifiedIllegalAccessException
- 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.public void setBoolean(Object obj, boolean z) throws IllegalArgumentException, IllegalAccessException
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
.
obj
- the object whose field should be modifiedz
- the new value for the field of obj
being modifiedIllegalAccessException
- 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.set(java.lang.Object, java.lang.Object)
public void setByte(Object obj, byte b) throws IllegalArgumentException, IllegalAccessException
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
.
obj
- the object whose field should be modifiedb
- the new value for the field of obj
being modifiedIllegalAccessException
- 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.set(java.lang.Object, java.lang.Object)
public void setChar(Object obj, char c) throws IllegalArgumentException, IllegalAccessException
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
.
obj
- the object whose field should be modifiedc
- the new value for the field of obj
being modifiedIllegalAccessException
- 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.set(java.lang.Object, java.lang.Object)
public void setShort(Object obj, short s) throws IllegalArgumentException, IllegalAccessException
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
.
obj
- the object whose field should be modifieds
- the new value for the field of obj
being modifiedIllegalAccessException
- 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.set(java.lang.Object, java.lang.Object)
public void setInt(Object obj, int i) throws IllegalArgumentException, IllegalAccessException
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
.
obj
- the object whose field should be modifiedi
- the new value for the field of obj
being modifiedIllegalAccessException
- 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.set(java.lang.Object, java.lang.Object)
public void setLong(Object obj, long l) throws IllegalArgumentException, IllegalAccessException
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
.
obj
- the object whose field should be modifiedl
- the new value for the field of obj
being modifiedIllegalAccessException
- 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.set(java.lang.Object, java.lang.Object)
public void setFloat(Object obj, float f) throws IllegalArgumentException, IllegalAccessException
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
.
obj
- the object whose field should be modifiedf
- the new value for the field of obj
being modifiedIllegalAccessException
- 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.set(java.lang.Object, java.lang.Object)
public void setDouble(Object obj, double d) throws IllegalArgumentException, IllegalAccessException
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
.
obj
- the object whose field should be modifiedd
- the new value for the field of obj
being modifiedIllegalAccessException
- 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.set(java.lang.Object, java.lang.Object)
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.
getAnnotation
in interface AnnotatedElement
getAnnotation
in class AccessibleObject
T
- the type of the annotation to query for and return if presentannotationClass
- the Class object corresponding to the annotation typeNullPointerException
- if the given annotation class is nullpublic <T extends Annotation> 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 AnnotatedElement.getAnnotation(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.
getAnnotationsByType
in interface AnnotatedElement
getAnnotationsByType
in class AccessibleObject
T
- the type of the annotation to query for and return if presentannotationClass
- the Class object corresponding to the annotation typeNullPointerException
- if the given annotation class is nullpublic 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.
getDeclaredAnnotations
in interface AnnotatedElement
getDeclaredAnnotations
in class AccessibleObject
public AnnotatedType getAnnotatedType()
Returns an AnnotatedType object that represents the use of a type to specify the declared type of the field represented by this Field.
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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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