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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

From interface java.lang.reflect.Member

Public methods

boolean equals(Object obj)

Compares this Field against the specified object.

Object get(Object obj)

Returns the value of the field represented by this Field, on the specified object.

<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 boolean field.

byte getByte(Object obj)

Gets the value of a static or instance byte field.

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.

Annotation[] getDeclaredAnnotations()

Returns annotations that are directly present on this element.

Class<?> getDeclaringClass()

Returns the Class object representing the class or interface that declares the field represented by this Field object.

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.

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.

Type getGenericType()

Returns a Type object that represents the declared type for the field represented by this Field object.

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.

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.

int getModifiers()

Returns the Java language modifiers for the field represented by this Field object, as an integer.

String getName()

Returns the name of the field represented by this Field object.

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.

Class<?> getType()

Returns a Class object that identifies the declared type for the field represented by this Field object.

int hashCode()

Returns a hashcode for this Field.

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 true if this field represents an element of an enumerated type; returns false otherwise.

boolean isSynthetic()

Returns true if this field is a synthetic field; returns false otherwise.

void set(Object obj, Object value)

Sets the field represented by this Field object on the specified object argument to the specified new value.

void setBoolean(Object obj, boolean z)

Sets the value of a field as a boolean on the specified object.

void setByte(Object obj, byte b)

Sets the value of a field as a byte on the specified object.

void setChar(Object obj, char c)

Sets the value of a field as a char on the specified object.

void setDouble(Object obj, double d)

Sets the value of a field as a double on the specified object.

void setFloat(Object obj, float f)

Sets the value of a field as a float on the specified object.

void setInt(Object obj, int i)

Sets the value of a field as an int on the specified object.

void setLong(Object obj, long l)

Sets the value of a field as a long on the specified object.

void setShort(Object obj, short s)

Sets the value of a field as a short on the specified object.

String toGenericString()

Returns a string describing this Field, including its generic type.

String toString()

Returns a string describing this Field.

Inherited methods

From class java.lang.reflect.AccessibleObject
From class java.lang.Object
From interface java.lang.reflect.AnnotatedElement
From interface java.lang.reflect.Member

Public methods

equals

added in API level 1
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

added in API level 1
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

added in API level 1
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

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(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

added in API level 1
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

added in API level 1
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

added in API level 1
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

added in API level 1
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

added in API level 1
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

added in API level 1
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

added in API level 1
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

added in API level 1
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

added in API level 1
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

added in API level 1
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

added in API level 1
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

added in API level 1
String getName ()

Returns the name of the field represented by this Field object.

Returns
String the simple name of the underlying member

getShort

added in API level 1
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

added in API level 1
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

added in API level 1
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

added in API level 1
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

added in API level 1
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

added in API level 1
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

added in API level 1
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, 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.

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

added in API level 1
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

added in API level 1
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

added in API level 1
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

added in API level 1
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

added in API level 1
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

added in API level 1
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

added in API level 1
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

added in API level 1
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

added in API level 1
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

added in API level 1
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

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