Java™ Platform
Standard Ed. 6

java.lang.reflect
Class Field

java.lang.Object
  extended by java.lang.reflect.AccessibleObject
      extended by java.lang.reflect.Field
All Implemented Interfaces:
AnnotatedElement, Member

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.

See Also:
Member, Class, Class.getFields(), Class.getField(String), Class.getDeclaredFields(), Class.getDeclaredField(String)

Field Summary
 
Fields inherited from interface java.lang.reflect.Member
DECLARED, PUBLIC
 
Method Summary
 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.
 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 all 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 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.
 
Methods inherited from class java.lang.reflect.AccessibleObject
getAnnotations, isAccessible, isAnnotationPresent, setAccessible, setAccessible
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
 

Method Detail

getDeclaringClass

public Class<?> getDeclaringClass()
Returns the Class object representing the class or interface that declares the field represented by this Field object.

Specified by:
getDeclaringClass in interface Member
Returns:
an object representing the declaring class of the underlying member

getName

public String getName()
Returns the name of the field represented by this Field object.

Specified by:
getName in interface Member
Returns:
the simple name of the underlying member

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.

Specified by:
getModifiers in interface Member
Returns:
the Java language modifiers for the underlying member
See Also:
Modifier

isEnumConstant

public boolean isEnumConstant()
Returns true if this field represents an element of an enumerated type; returns false otherwise.

Returns:
true if and only if this field represents an element of an enumerated type.
Since:
1.5

isSynthetic

public boolean isSynthetic()
Returns true if this field is a synthetic field; returns false otherwise.

Specified by:
isSynthetic in interface Member
Returns:
true if and only if this field is a synthetic field as defined by the Java Language Specification.
Since:
1.5

getType

public Class<?> getType()
Returns a Class object that identifies the declared type for the field represented by this Field object.

Returns:
a Class object identifying the declared type of the field represented by this object

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:
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, 3rd edition
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
Since:
1.5

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.

Overrides:
equals in class Object
Parameters:
obj - the reference object with which to compare.
Returns:
true if this object is the same as the obj argument; false otherwise.
See Also:
Object.hashCode(), Hashtable

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.

Overrides:
hashCode in class Object
Returns:
a hash code value for this object.
See Also:
Object.equals(java.lang.Object), Hashtable

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.

Overrides:
toString in class Object
Returns:
a string representation of the object.

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:
a string describing this Field, including its generic type
Since:
1.5

get

public 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 enforces 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 from which the represented field's value is to be extracted
Returns:
the value of the represented field in object obj; primitive values are wrapped in an appropriate object before being returned
Throws:
IllegalAccessException - if the underlying field is inaccessible.
IllegalArgumentException - if the specified object is not an instance of the class or interface declaring the underlying field (or a subclass or implementor thereof).
NullPointerException - if the specified object is null and the field is an instance field.
ExceptionInInitializerError - if the initialization provoked by this method fails.

getBoolean

public boolean getBoolean(Object obj)
                   throws IllegalArgumentException,
                          IllegalAccessException
Gets the value of a static or instance boolean field.

Parameters:
obj - the object to extract the boolean value from
Returns:
the value of the boolean field
Throws:
IllegalAccessException - if 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:
get(java.lang.Object)

getByte

public byte getByte(Object obj)
             throws IllegalArgumentException,
                    IllegalAccessException
Gets the value of a static or instance byte field.

Parameters:
obj - the object to extract the byte value from
Returns:
the value of the byte field
Throws:
IllegalAccessException - if 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:
get(java.lang.Object)

getChar

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.

Parameters:
obj - the object to extract the char value from
Returns:
the value of the field converted to type char
Throws:
IllegalAccessException - if 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:
get(java.lang.Object)

getShort

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.

Parameters:
obj - the object to extract the short value from
Returns:
the value of the field converted to type short
Throws:
IllegalAccessException - if 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:
get(java.lang.Object)

getInt

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.

Parameters:
obj - the object to extract the int value from
Returns:
the value of the field converted to type int
Throws:
IllegalAccessException - if 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:
get(java.lang.Object)

getLong

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.

Parameters:
obj - the object to extract the long value from
Returns:
the value of the field converted to type long
Throws:
IllegalAccessException - if 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:
get(java.lang.Object)

getFloat

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.

Parameters:
obj - the object to extract the float value from
Returns:
the value of the field converted to type float
Throws:
IllegalAccessException - if 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:
get(java.lang.Object)

getDouble

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.

Parameters:
obj - the object to extract the double value from
Returns:
the value of the field converted to type double
Throws:
IllegalAccessException - if 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:
get(java.lang.Object)

set

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 enforces 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 and this field is non-static. Setting a final field in this way is meaningful only during deserialization or reconstruction of instances of classes with blank final fields, before they are made available for access by other parts of a program. Use in any other context may have unpredictable effects, including cases in which other parts of a program continue to use the original value of this field.

If the underlying field is of a primitive type, an unwrapping conversion is attempted to convert the new value to a value of a primitive type. If this attempt fails, the method throws an IllegalArgumentException.

If, after possible unwrapping, the new value cannot be converted to the type of the underlying field by an identity or widening conversion, the method throws an IllegalArgumentException.

If the underlying field is static, the class that declared the field is initialized if it has not already been initialized.

The field is set to the possibly unwrapped and widened new value.

If the field is hidden in the type of obj, the field's value is set according to the preceding rules.

Parameters:
obj - the object whose field should be modified
value - the new value for the field of obj being modified
Throws:
IllegalAccessException - if 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 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)
                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.

Parameters:
obj - the object whose field should be modified
z - the new value for the field of obj being modified
Throws:
IllegalAccessException - if 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 an unwrapping conversion fails.
NullPointerException - if the specified object is null and the field is an instance field.
ExceptionInInitializerError - if the initialization provoked by this method fails.
See Also:
set(java.lang.Object, java.lang.Object)

setByte

public void setByte(Object obj,
                    byte b)
             throws IllegalArgumentException,
                    IllegalAccessException
Sets the value of a field as 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 - the object whose field should be modified
b - the new value for the field of obj being modified
Throws:
IllegalAccessException - if 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 an unwrapping conversion fails.
NullPointerException - if the specified object is null and the field is an instance field.
ExceptionInInitializerError - if the initialization provoked by this method fails.
See Also:
set(java.lang.Object, java.lang.Object)

setChar

public void setChar(Object obj,
                    char c)
             throws IllegalArgumentException,
                    IllegalAccessException
Sets the value of a field as 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 - the object whose field should be modified
c - the new value for the field of obj being modified
Throws:
IllegalAccessException - if 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 an unwrapping conversion fails.
NullPointerException - if the specified object is null and the field is an instance field.
ExceptionInInitializerError - if the initialization provoked by this method fails.
See Also:
set(java.lang.Object, java.lang.Object)

setShort

public void setShort(Object obj,
                     short s)
              throws IllegalArgumentException,
                     IllegalAccessException
Sets the value of a field as 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 - the object whose field should be modified
s - the new value for the field of obj being modified
Throws:
IllegalAccessException - if 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 an unwrapping conversion fails.
NullPointerException - if the specified object is null and the field is an instance field.
ExceptionInInitializerError - if the initialization provoked by this method fails.
See Also:
set(java.lang.Object, java.lang.Object)

setInt

public void setInt(Object obj,
                   int i)
            throws IllegalArgumentException,
                   IllegalAccessException
Sets the value of a field as 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 - the object whose field should be modified
i - the new value for the field of obj being modified
Throws:
IllegalAccessException - if 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 an unwrapping conversion fails.
NullPointerException - if the specified object is null and the field is an instance field.
ExceptionInInitializerError - if the initialization provoked by this method fails.
See Also:
set(java.lang.Object, java.lang.Object)

setLong

public void setLong(Object obj,
                    long l)
             throws IllegalArgumentException,
                    IllegalAccessException
Sets the value of a field as 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 - the object whose field should be modified
l - the new value for the field of obj being modified
Throws:
IllegalAccessException - if 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 an unwrapping conversion fails.
NullPointerException - if the specified object is null and the field is an instance field.
ExceptionInInitializerError - if the initialization provoked by this method fails.
See Also:
set(java.lang.Object, java.lang.Object)

setFloat

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.

Parameters:
obj - the object whose field should be modified
f - the new value for the field of obj being modified
Throws:
IllegalAccessException - if 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 an unwrapping conversion fails.
NullPointerException - if the specified object is null and the field is an instance field.
ExceptionInInitializerError - if the initialization provoked by this method fails.
See Also:
set(java.lang.Object, java.lang.Object)

setDouble

public void setDouble(Object obj,
                      double d)
               throws IllegalArgumentException,
                      IllegalAccessException
Sets the value of a field as 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 - the object whose field should be modified
d - the new value for the field of obj being modified
Throws:
IllegalAccessException - if 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 an unwrapping conversion fails.
NullPointerException - if the specified object is null and the field is an instance field.
ExceptionInInitializerError - if the initialization provoked by this method fails.
See Also:
set(java.lang.Object, java.lang.Object)

getAnnotation

public <T extends Annotation> T getAnnotation(Class<T> annotationClass)
Description copied from interface: AnnotatedElement
Returns this element's annotation for the specified type if such an annotation is present, else null.

Specified by:
getAnnotation in interface AnnotatedElement
Overrides:
getAnnotation in class AccessibleObject
Parameters:
annotationClass - the Class object corresponding to the annotation type
Returns:
this element's annotation for the specified annotation type if present on this element, else null
Throws:
NullPointerException - if the given annotation class is null
Since:
1.5

getDeclaredAnnotations

public Annotation[] getDeclaredAnnotations()
Description copied from interface: AnnotatedElement
Returns all annotations that are directly present on this element. Unlike the other methods in this interface, this method ignores inherited annotations. (Returns an array of length zero if no annotations are directly present on this element.) The caller of this method is free to modify the returned array; it will have no effect on the arrays returned to other callers.

Specified by:
getDeclaredAnnotations in interface AnnotatedElement
Overrides:
getDeclaredAnnotations in class AccessibleObject
Returns:
All annotations directly present on this element
Since:
1.5

Java™ Platform
Standard Ed. 6

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