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 |
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Public methods | |
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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 | |
|---|---|
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 thisFieldobject;- 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 |