java.lang.reflect

Class Field

java.lang.Object

java.lang.reflect.AccessibleObject

java.lang.reflect.Field

All Implemented Interfaces:

AnnotatedElement, Member

public final class Field
extends AccessibleObject
implements Member

The Field class represents a member variable of a class. It also allows dynamic access to a member, via reflection. This works for both static and instance fields. Operations on Field objects know how to do widening conversions, but throw IllegalArgumentException if a narrowing conversion would be necessary. You can query for information on this Field regardless of location, but get and set access may be limited by Java language access controls. If you can't do it in the compiler, you can't normally do it here either.

Note: This class returns and accepts types as Classes, even primitive types; there are Class types defined that represent each different primitive type. They are java.lang.Boolean.TYPE, java.lang.Byte.TYPE,, also available as boolean.class, byte.class, etc. These are not to be confused with the classes java.lang.Boolean, java.lang.Byte, etc., which are real classes.

Also note that this is not a serializable class. It is entirely feasible to make it serializable using the Externalizable interface, but this is on Sun, not me.

Since:

1.1

See Also:

Member, Class, Class.getField(String), Class.getDeclaredField(String), Class.getFields(), Class.getDeclaredFields()

Field Summary

Fields inherited from interface java.lang.reflect.Member

DECLARED, PUBLIC

Method Summary

Methods

Modifier and Type	Method and Description
boolean	equals(java.lang.Object o) Compare two objects to see if they are semantically equivalent.
java.lang.Object	get(java.lang.Object o) Get the value of this Field.
<T extends java.lang.annotation.Annotation> T	getAnnotation(java.lang.Class<T> annotationClass) Returns the element's annotation for the specified annotation type, or null if no such annotation exists.
boolean	getBoolean(java.lang.Object o) Get the value of this boolean Field.
byte	getByte(java.lang.Object o) Get the value of this byte Field.
char	getChar(java.lang.Object o) Get the value of this Field as a char.
java.lang.annotation.Annotation[]	getDeclaredAnnotations() Returns all annotations directly defined by the element.
java.lang.Class<?>	getDeclaringClass() Gets the class that declared this field, or the class where this field is a non-inherited member.
double	getDouble(java.lang.Object o) Get the value of this Field as a double.
float	getFloat(java.lang.Object o) Get the value of this Field as a float.
Type	getGenericType() Return the generic type of the field.
int	getInt(java.lang.Object o) Get the value of this Field as an int.
long	getLong(java.lang.Object o) Get the value of this Field as a long.
int	getModifiers() Gets the modifiers this field uses.
java.lang.String	getName() Gets the name of this field.
short	getShort(java.lang.Object o) Get the value of this Field as a short.
java.lang.Class<?>	getType() Gets the type of this field.
int	hashCode() Get the hash code for the Field.
boolean	isEnumConstant() Return true if this field represents an enum constant, false otherwise.
boolean	isSynthetic() Return true if this field is synthetic, false otherwise.
void	set(java.lang.Object o, java.lang.Object value) Set the value of this Field.
void	setBoolean(java.lang.Object o, boolean value) Set this boolean Field.
void	setByte(java.lang.Object o, byte value) Set this byte Field.
void	setChar(java.lang.Object o, char value) Set this char Field.
void	setDouble(java.lang.Object o, double value) Set this double Field.
void	setFloat(java.lang.Object o, float value) Set this float Field.
void	setInt(java.lang.Object o, int value) Set this int Field.
void	setLong(java.lang.Object o, long value) Set this long Field.
void	setShort(java.lang.Object o, short value) Set this short Field.
java.lang.String	toGenericString()
java.lang.String	toString() Get a String representation of the 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 java.lang.Class<?> getDeclaringClass()

Gets the class that declared this field, or the class where this field is a non-inherited member.

Specified by:

getDeclaringClass in interface Member

Returns:

the class that declared this member

getName

public java.lang.String getName()

Gets the name of this field.

Specified by:

getName in interface Member

Returns:

the name of this field

getModifiers

public int getModifiers()

Gets the modifiers this field uses. Use the Modifier class to interpret the values. A field can only have a subset of the following modifiers: public, private, protected, static, final, transient, and volatile.

Specified by:

getModifiers in interface Member

Returns:

an integer representing the modifiers to this Member

See Also:

Modifier

isSynthetic

public boolean isSynthetic()

Return true if this field is synthetic, false otherwise.

Specified by:

isSynthetic in interface Member

Returns:

true if the member is synthetic

Since:

1.5

isEnumConstant

public boolean isEnumConstant()

Return true if this field represents an enum constant, false otherwise.

Since:

1.5

getType

public java.lang.Class<?> getType()

Gets the type of this field.

Returns:

the type of this field

equals

public boolean equals(java.lang.Object o)

Compare two objects to see if they are semantically equivalent. Two Fields are semantically equivalent if they have the same declaring class, name, and type. Since you can't creat a Field except through the VM, this is just the == relation.

Overrides:

equals in class java.lang.Object

Parameters:

o - the object to compare to

Returns:

true if they are equal; false if not

See Also:

Object.hashCode()

hashCode

public int hashCode()

Get the hash code for the Field. The Field hash code is the hash code of its name XOR'd with the hash code of its class name.

Overrides:

hashCode in class java.lang.Object

Returns:

the hash code for the object.

See Also:

Object.equals(Object), System.identityHashCode(Object)

toString

public java.lang.String toString()

Get a String representation of the Field. A Field's String representation is "<modifiers> <type> <class>.<fieldname>".
Example: public transient boolean gnu.parse.Parser.parseComplete

Overrides:

toString in class java.lang.Object

Returns:

the String representation of the Field

See Also:

Object.getClass(), Object.hashCode(), Class.getName(), Integer.toHexString(int)

toGenericString

public java.lang.String toGenericString()

get

public java.lang.Object get(java.lang.Object o)
                     throws java.lang.IllegalAccessException

Get the value of this Field. If it is primitive, it will be wrapped in the appropriate wrapper type (boolean = java.lang.Boolean).

If the field is static, o will be ignored. Otherwise, if o is null, you get a NullPointerException, and if it is incompatible with the declaring class of the field, you get an IllegalArgumentException.

Next, if this Field enforces access control, your runtime context is evaluated, and you may have an IllegalAccessException if you could not access this field in similar compiled code. If the field is static, and its class is uninitialized, you trigger class initialization, which may end in a ExceptionInInitializerError.

Finally, the field is accessed, and primitives are wrapped (but not necessarily in new objects). This method accesses the field of the declaring class, even if the instance passed in belongs to a subclass which declares another field to hide this one.

Parameters:

o - the object to get the value of this Field from

Returns:

the value of the Field

Throws:

java.lang.IllegalAccessException - if you could not normally access this field (i.e. it is not public)

java.lang.IllegalArgumentException - if o is not an instance of the class or interface declaring this field

java.lang.NullPointerException - if o is null and this field requires an instance

java.lang.ExceptionInInitializerError - if accessing a static field triggered class initialization, which then failed

See Also:

getBoolean(Object), getByte(Object), getChar(Object), getShort(Object), getInt(Object), getLong(Object), getFloat(Object), getDouble(Object)

getBoolean

public boolean getBoolean(java.lang.Object o)
                   throws java.lang.IllegalAccessException

Get the value of this boolean Field. If the field is static, o will be ignored.

Parameters:

o - the object to get the value of this Field from

Returns:

the value of the Field

Throws:

java.lang.IllegalAccessException - if you could not normally access this field (i.e. it is not public)

java.lang.IllegalArgumentException - if this is not a boolean field of o, or if o is not an instance of the declaring class of this field

java.lang.NullPointerException - if o is null and this field requires an instance

java.lang.ExceptionInInitializerError - if accessing a static field triggered class initialization, which then failed

See Also:

get(Object)

getByte

public byte getByte(java.lang.Object o)
             throws java.lang.IllegalAccessException

Get the value of this byte Field. If the field is static, o will be ignored.

Parameters:

o - the object to get the value of this Field from

Returns:

the value of the Field

Throws:

java.lang.IllegalAccessException - if you could not normally access this field (i.e. it is not public)

java.lang.IllegalArgumentException - if this is not a byte field of o, or if o is not an instance of the declaring class of this field

java.lang.NullPointerException - if o is null and this field requires an instance

java.lang.ExceptionInInitializerError - if accessing a static field triggered class initialization, which then failed

See Also:

get(Object)

getChar

public char getChar(java.lang.Object o)
             throws java.lang.IllegalAccessException

Get the value of this Field as a char. If the field is static, o will be ignored.

Throws:

java.lang.IllegalAccessException - if you could not normally access this field (i.e. it is not public)

java.lang.IllegalArgumentException - if this is not a char field of o, or if o is not an instance of the declaring class of this field

java.lang.NullPointerException - if o is null and this field requires an instance

java.lang.ExceptionInInitializerError - if accessing a static field triggered class initialization, which then failed

See Also:

get(Object)

getShort

public short getShort(java.lang.Object o)
               throws java.lang.IllegalAccessException

Get the value of this Field as a short. If the field is static, o will be ignored.

Parameters:

o - the object to get the value of this Field from

Returns:

the value of the Field

Throws:

java.lang.IllegalAccessException - if you could not normally access this field (i.e. it is not public)

java.lang.IllegalArgumentException - if this is not a byte or short field of o, or if o is not an instance of the declaring class of this field

java.lang.NullPointerException - if o is null and this field requires an instance

java.lang.ExceptionInInitializerError - if accessing a static field triggered class initialization, which then failed

See Also:

get(Object)

getInt

public int getInt(java.lang.Object o)
           throws java.lang.IllegalAccessException

Get the value of this Field as an int. If the field is static, o will be ignored.

Parameters:

o - the object to get the value of this Field from

Returns:

the value of the Field

Throws:

java.lang.IllegalAccessException - if you could not normally access this field (i.e. it is not public)

java.lang.IllegalArgumentException - if this is not a byte, short, char, or int field of o, or if o is not an instance of the declaring class of this field

java.lang.NullPointerException - if o is null and this field requires an instance

java.lang.ExceptionInInitializerError - if accessing a static field triggered class initialization, which then failed

See Also:

get(Object)

getLong

public long getLong(java.lang.Object o)
             throws java.lang.IllegalAccessException

Get the value of this Field as a long. If the field is static, o will be ignored.

Parameters:

o - the object to get the value of this Field from

Returns:

the value of the Field

Throws:

java.lang.IllegalAccessException - if you could not normally access this field (i.e. it is not public)

java.lang.IllegalArgumentException - if this is not a byte, short, char, int, or long field of o, or if o is not an instance of the declaring class of this field

java.lang.NullPointerException - if o is null and this field requires an instance

java.lang.ExceptionInInitializerError - if accessing a static field triggered class initialization, which then failed

See Also:

get(Object)

getFloat

public float getFloat(java.lang.Object o)
               throws java.lang.IllegalAccessException

Get the value of this Field as a float. If the field is static, o will be ignored.

Parameters:

o - the object to get the value of this Field from

Returns:

the value of the Field

Throws:

java.lang.IllegalAccessException - if you could not normally access this field (i.e. it is not public)

java.lang.IllegalArgumentException - if this is not a byte, short, char, int, long, or float field of o, or if o is not an instance of the declaring class of this field

java.lang.NullPointerException - if o is null and this field requires an instance

java.lang.ExceptionInInitializerError - if accessing a static field triggered class initialization, which then failed

See Also:

get(Object)

getDouble

public double getDouble(java.lang.Object o)
                 throws java.lang.IllegalAccessException

Get the value of this Field as a double. If the field is static, o will be ignored.

Parameters:

o - the object to get the value of this Field from

Returns:

the value of the Field

Throws:

java.lang.IllegalAccessException - if you could not normally access this field (i.e. it is not public)

java.lang.IllegalArgumentException - if this is not a byte, short, char, int, long, float, or double field of o, or if o is not an instance of the declaring class of this field

java.lang.NullPointerException - if o is null and this field requires an instance

java.lang.ExceptionInInitializerError - if accessing a static field triggered class initialization, which then failed

See Also:

get(Object)

set

public void set(java.lang.Object o,
       java.lang.Object value)
         throws java.lang.IllegalAccessException

Set the value of this Field. If it is a primitive field, the value will be unwrapped from the passed object (boolean = java.lang.Boolean).

If the field is static, o will be ignored. Otherwise, if o is null, you get a NullPointerException, and if it is incompatible with the declaring class of the field, you get an IllegalArgumentException.

Next, if this Field enforces access control, your runtime context is evaluated, and you may have an IllegalAccessException if you could not access this field in similar compiled code. This also occurs whether or not there is access control if the field is final. If the field is primitive, and unwrapping your argument fails, you will get an IllegalArgumentException; likewise, this error happens if value cannot be cast to the correct object type. If the field is static, and its class is uninitialized, you trigger class initialization, which may end in a ExceptionInInitializerError.

Finally, the field is set with the widened value. This method accesses the field of the declaring class, even if the instance passed in belongs to a subclass which declares another field to hide this one.

Parameters:

o - the object to set this Field on

value - the value to set this Field to

Throws:

java.lang.IllegalAccessException - if you could not normally access this field (i.e. it is not public)

java.lang.IllegalArgumentException - if value cannot be converted by a widening conversion to the underlying type of the Field, or if o is not an instance of the class declaring this field

java.lang.NullPointerException - if o is null and this field requires an instance

java.lang.ExceptionInInitializerError - if accessing a static field triggered class initialization, which then failed

See Also:

setBoolean(Object, boolean), setByte(Object, byte), setChar(Object, char), setShort(Object, short), setInt(Object, int), setLong(Object, long), setFloat(Object, float), setDouble(Object, double)

setBoolean

public void setBoolean(java.lang.Object o,
              boolean value)
                throws java.lang.IllegalAccessException

Set this boolean Field. If the field is static, o will be ignored.

Parameters:

o - the object to set this Field on

value - the value to set this Field to

Throws:

java.lang.IllegalAccessException - if you could not normally access this field (i.e. it is not public)

java.lang.IllegalArgumentException - if this is not a boolean field, or if o is not an instance of the class declaring this field

java.lang.NullPointerException - if o is null and this field requires an instance

java.lang.ExceptionInInitializerError - if accessing a static field triggered class initialization, which then failed

See Also:

set(Object, Object)

setByte

public void setByte(java.lang.Object o,
           byte value)
             throws java.lang.IllegalAccessException

Set this byte Field. If the field is static, o will be ignored.

Parameters:

o - the object to set this Field on

value - the value to set this Field to

Throws:

java.lang.IllegalAccessException - if you could not normally access this field (i.e. it is not public)

java.lang.IllegalArgumentException - if this is not a byte, short, int, long, float, or double field, or if o is not an instance of the class declaring this field

java.lang.NullPointerException - if o is null and this field requires an instance

java.lang.ExceptionInInitializerError - if accessing a static field triggered class initialization, which then failed

See Also:

set(Object, Object)

setChar

public void setChar(java.lang.Object o,
           char value)
             throws java.lang.IllegalAccessException

Set this char Field. If the field is static, o will be ignored.

Parameters:

o - the object to set this Field on

value - the value to set this Field to

Throws:

java.lang.IllegalAccessException - if you could not normally access this field (i.e. it is not public)

java.lang.IllegalArgumentException - if this is not a char, int, long, float, or double field, or if o is not an instance of the class declaring this field

java.lang.NullPointerException - if o is null and this field requires an instance

java.lang.ExceptionInInitializerError - if accessing a static field triggered class initialization, which then failed

See Also:

set(Object, Object)

setShort

public void setShort(java.lang.Object o,
            short value)
              throws java.lang.IllegalAccessException

Set this short Field. If the field is static, o will be ignored.

Parameters:

o - the object to set this Field on

value - the value to set this Field to

Throws:

java.lang.IllegalAccessException - if you could not normally access this field (i.e. it is not public)

java.lang.IllegalArgumentException - if this is not a short, int, long, float, or double field, or if o is not an instance of the class declaring this field

java.lang.NullPointerException - if o is null and this field requires an instance

java.lang.ExceptionInInitializerError - if accessing a static field triggered class initialization, which then failed

See Also:

set(Object, Object)

setInt

public void setInt(java.lang.Object o,
          int value)
            throws java.lang.IllegalAccessException

Set this int Field. If the field is static, o will be ignored.

Parameters:

o - the object to set this Field on

value - the value to set this Field to

Throws:

java.lang.IllegalAccessException - if you could not normally access this field (i.e. it is not public)

java.lang.IllegalArgumentException - if this is not an int, long, float, or double field, or if o is not an instance of the class declaring this field

java.lang.NullPointerException - if o is null and this field requires an instance

java.lang.ExceptionInInitializerError - if accessing a static field triggered class initialization, which then failed

See Also:

set(Object, Object)

setLong

public void setLong(java.lang.Object o,
           long value)
             throws java.lang.IllegalAccessException

Set this long Field. If the field is static, o will be ignored.

Parameters:

o - the object to set this Field on

value - the value to set this Field to

Throws:

java.lang.IllegalAccessException - if you could not normally access this field (i.e. it is not public)

java.lang.IllegalArgumentException - if this is not a long, float, or double field, or if o is not an instance of the class declaring this field

java.lang.NullPointerException - if o is null and this field requires an instance

java.lang.ExceptionInInitializerError - if accessing a static field triggered class initialization, which then failed

See Also:

set(Object, Object)

setFloat

public void setFloat(java.lang.Object o,
            float value)
              throws java.lang.IllegalAccessException

Set this float Field. If the field is static, o will be ignored.

Parameters:

o - the object to set this Field on

value - the value to set this Field to

Throws:

java.lang.IllegalAccessException - if you could not normally access this field (i.e. it is not public)

java.lang.IllegalArgumentException - if this is not a float or long field, or if o is not an instance of the class declaring this field

java.lang.NullPointerException - if o is null and this field requires an instance

java.lang.ExceptionInInitializerError - if accessing a static field triggered class initialization, which then failed

See Also:

set(Object, Object)

setDouble

public void setDouble(java.lang.Object o,
             double value)
               throws java.lang.IllegalAccessException

Set this double Field. If the field is static, o will be ignored.

Parameters:

o - the object to set this Field on

value - the value to set this Field to

Throws:

java.lang.IllegalAccessException - if you could not normally access this field (i.e. it is not public)

java.lang.IllegalArgumentException - if this is not a double field, or if o is not an instance of the class declaring this field

java.lang.NullPointerException - if o is null and this field requires an instance

java.lang.ExceptionInInitializerError - if accessing a static field triggered class initialization, which then failed

See Also:

set(Object, Object)

getGenericType

public Type getGenericType()

Return the generic type of the field. If the field type is not a generic type, the method returns the same as getType().

Throws:

GenericSignatureFormatError - if the generic signature does not conform to the format specified in the Virtual Machine specification, version 3.

Since:

1.5

getAnnotation

public <T extends java.lang.annotation.Annotation> T getAnnotation(java.lang.Class<T> annotationClass)

Returns the element's annotation for the specified annotation type, or null if no such annotation exists.

Specified by:

getAnnotation in interface AnnotatedElement

Overrides:

getAnnotation in class AccessibleObject

Parameters:

annotationClass - the type of annotation to look for.

Returns:

this element's annotation for the specified type, or null if no such annotation exists.

Throws:

java.lang.NullPointerException - if the annotation class is null.

getDeclaredAnnotations

public java.lang.annotation.Annotation[] getDeclaredAnnotations()

Returns all annotations directly defined by the element. If there are no annotations directly associated with the element, then a zero-length array will be returned. The returned array may be modified by the client code, but this will have no effect on the annotation content of this class, and hence no effect on the return value of this method for future callers.

Specified by:

getDeclaredAnnotations in interface AnnotatedElement

Overrides:

getDeclaredAnnotations in class AccessibleObject

Returns:

the annotations directly defined by the element.

Since:

1.5