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java.lang.reflect

Class Field

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()

Fields inherited from interface java.lang.reflect.Member

DECLARED, PUBLIC

Method Summary

boolean
equals(Object fld)
Compare two objects to see if they are semantically equivalent.
extends Annotation> T getAnnotation(Class annoClass)
Object
get(Object obj)
Get the value of this Field.
boolean
getBoolean(Object obj)
Get the value of this boolean Field.
byte
getByte(Object obj)
Get the value of this byte Field.
char
getChar(Object obj)
Get the value of this Field as a char.
Annotation[]
getDeclaredAnnotations()
Class
getDeclaringClass()
Gets the class that declared this field, or the class where this field is a non-inherited member.
double
getDouble(Object obj)
Get the value of this Field as a double.
float
getFloat(Object obj)
Get the value of this Field as a float.
Type
getGenericType()
Return the generic type of the field.
int
getInt(Object obj)
Get the value of this Field as an int.
long
getLong(Object obj)
Get the value of this Field as a long.
int
getModifiers()
Gets the modifiers this field uses.
String
getName()
Gets the name of this field.
short
getShort(Object obj)
Get the value of this Field as a short.
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(Object object, Object value)
Set the value of this Field.
void
setBoolean(Object obj, boolean b)
Set this boolean Field.
void
setByte(Object obj, byte b)
Set this byte Field.
void
setChar(Object obj, char c)
Set this char Field.
void
setDouble(Object obj, double d)
Set this double Field.
void
setFloat(Object obj, float f)
Set this float Field.
void
setInt(Object obj, int i)
Set this int Field.
void
setLong(Object obj, long l)
Set this long Field.
void
setShort(Object obj, short s)
Set this short Field.
String
toGenericString()
String
toString()
Get a String representation of the Field.

Methods inherited from class java.lang.reflect.AccessibleObject

extends Annotation> T getAnnotation, getAnnotations, getDeclaredAnnotations, isAccessible, isAnnotationPresent, setAccessible, setAccessible

Methods inherited from class java.lang.Object

clone, equals, extends Object> getClass, finalize, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Details

equals

public boolean equals(Object fld)
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 interface Object
Parameters:
Returns:
true if they are equal; false if not

extends Annotation> T getAnnotation

public extends Annotation> T getAnnotation(Class annoClass)
Specified by:
extends Annotation> T getAnnotation in interface AnnotatedElement
Overrides:
extends Annotation> T getAnnotation in interface AccessibleObject

get

public Object get(Object obj)
            throws 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:
Returns:
the value of the Field
Throws:
IllegalAccessException - if you could not normally access this field (i.e. it is not public)
IllegalArgumentException - if o is not an instance of the class or interface declaring this field
NullPointerException - if o is null and this field requires an instance
See Also:
getBoolean(Object), getByte(Object), getChar(Object), getShort(Object), getInt(Object), getLong(Object), getFloat(Object), getDouble(Object)

getBoolean

public boolean getBoolean(Object obj)
            throws IllegalAccessException
Get the value of this boolean Field. If the field is static, o will be ignored.
Parameters:
Returns:
the value of the Field
Throws:
IllegalAccessException - if you could not normally access this field (i.e. it is not public)
IllegalArgumentException - if this is not a boolean field of o, or if o is not an instance of the declaring class of this field
NullPointerException - if o is null and this field requires an instance
See Also:
get(Object)

getByte

public byte getByte(Object obj)
            throws IllegalAccessException
Get the value of this byte Field. If the field is static, o will be ignored.
Parameters:
Returns:
the value of the Field
Throws:
IllegalAccessException - if you could not normally access this field (i.e. it is not public)
IllegalArgumentException - if this is not a byte field of o, or if o is not an instance of the declaring class of this field
NullPointerException - if o is null and this field requires an instance
See Also:
get(Object)

getChar

public char getChar(Object obj)
            throws IllegalAccessException
Get the value of this Field as a char. If the field is static, o will be ignored.
Throws:
IllegalAccessException - if you could not normally access this field (i.e. it is not public)
IllegalArgumentException - if this is not a char field of o, or if o is not an instance of the declaring class of this field
NullPointerException - if o is null and this field requires an instance
See Also:
get(Object)

getDeclaredAnnotations

public Annotation[] getDeclaredAnnotations()
Specified by:
getDeclaredAnnotations in interface AnnotatedElement
Overrides:
getDeclaredAnnotations in interface AccessibleObject

getDeclaringClass

public 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

getDouble

public double getDouble(Object obj)
            throws IllegalAccessException
Get the value of this Field as a double. If the field is static, o will be ignored.
Parameters:
Returns:
the value of the Field
Throws:
IllegalAccessException - if you could not normally access this field (i.e. it is not public)
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
NullPointerException - if o is null and this field requires an instance
See Also:
get(Object)

getFloat

public float getFloat(Object obj)
            throws IllegalAccessException
Get the value of this Field as a float. If the field is static, o will be ignored.
Parameters:
Returns:
the value of the Field
Throws:
IllegalAccessException - if you could not normally access this field (i.e. it is not public)
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
NullPointerException - if o is null and this field requires an instance
See Also:
get(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().
Since:
1.5

getInt

public int getInt(Object obj)
            throws IllegalAccessException
Get the value of this Field as an int. If the field is static, o will be ignored.
Parameters:
Returns:
the value of the Field
Throws:
IllegalAccessException - if you could not normally access this field (i.e. it is not public)
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
NullPointerException - if o is null and this field requires an instance
See Also:
get(Object)

getLong

public long getLong(Object obj)
            throws IllegalAccessException
Get the value of this Field as a long. If the field is static, o will be ignored.
Parameters:
Returns:
the value of the Field
Throws:
IllegalAccessException - if you could not normally access this field (i.e. it is not public)
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
NullPointerException - if o is null and this field requires an instance
See Also:
get(Object)

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

getName

public String getName()
Gets the name of this field.
Specified by:
getName in interface Member
Returns:
the name of this field

getShort

public short getShort(Object obj)
            throws IllegalAccessException
Get the value of this Field as a short. If the field is static, o will be ignored.
Parameters:
Returns:
the value of the Field
Throws:
IllegalAccessException - if you could not normally access this field (i.e. it is not public)
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
NullPointerException - if o is null and this field requires an instance
See Also:
get(Object)

getType

public Class getType()
Gets the type of this field.
Returns:
the type of this field

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 interface Object
Returns:
the hash code for the object.

isEnumConstant

public boolean isEnumConstant()
Return true if this field represents an enum constant, false otherwise.
Since:
1.5

isSynthetic

public boolean isSynthetic()
Return true if this field is synthetic, false otherwise.
Specified by:
isSynthetic in interface Member
Since:
1.5

set

public void set(Object object,
                Object value)
            throws 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:
value - the value to set this Field to
Throws:
IllegalAccessException - if you could not normally access this field (i.e. it is not public)
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
NullPointerException - if o is null and this field requires an instance
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(Object obj,
                       boolean b)
            throws IllegalAccessException
Set this boolean Field. If the field is static, o will be ignored.
Parameters:
Throws:
IllegalAccessException - if you could not normally access this field (i.e. it is not public)
IllegalArgumentException - if this is not a boolean field, or if o is not an instance of the class declaring this field
NullPointerException - if o is null and this field requires an instance
See Also:
set(Object,Object)

setByte

public void setByte(Object obj,
                    byte b)
            throws IllegalAccessException
Set this byte Field. If the field is static, o will be ignored.
Parameters:
Throws:
IllegalAccessException - if you could not normally access this field (i.e. it is not public)
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
NullPointerException - if o is null and this field requires an instance
See Also:
set(Object,Object)

setChar

public void setChar(Object obj,
                    char c)
            throws IllegalAccessException
Set this char Field. If the field is static, o will be ignored.
Parameters:
Throws:
IllegalAccessException - if you could not normally access this field (i.e. it is not public)
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
NullPointerException - if o is null and this field requires an instance
See Also:
set(Object,Object)

setDouble

public void setDouble(Object obj,
                      double d)
            throws IllegalAccessException
Set this double Field. If the field is static, o will be ignored.
Parameters:
Throws:
IllegalAccessException - if you could not normally access this field (i.e. it is not public)
IllegalArgumentException - if this is not a double field, or if o is not an instance of the class declaring this field
NullPointerException - if o is null and this field requires an instance
See Also:
set(Object,Object)

setFloat

public void setFloat(Object obj,
                     float f)
            throws IllegalAccessException
Set this float Field. If the field is static, o will be ignored.
Parameters:
Throws:
IllegalAccessException - if you could not normally access this field (i.e. it is not public)
IllegalArgumentException - if this is not a float or long field, or if o is not an instance of the class declaring this field
NullPointerException - if o is null and this field requires an instance
See Also:
set(Object,Object)

setInt

public void setInt(Object obj,
                   int i)
            throws IllegalAccessException
Set this int Field. If the field is static, o will be ignored.
Parameters:
Throws:
IllegalAccessException - if you could not normally access this field (i.e. it is not public)
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
NullPointerException - if o is null and this field requires an instance
See Also:
set(Object,Object)

setLong

public void setLong(Object obj,
                    long l)
            throws IllegalArgumentException,
                   IllegalAccessException
Set this long Field. If the field is static, o will be ignored.
Parameters:
Throws:
IllegalAccessException - if you could not normally access this field (i.e. it is not public)
IllegalArgumentException - if this is not a long, float, or double field, or if o is not an instance of the class declaring this field
NullPointerException - if o is null and this field requires an instance
See Also:
set(Object,Object)

setShort

public void setShort(Object obj,
                     short s)
            throws IllegalAccessException
Set this short Field. If the field is static, o will be ignored.
Parameters:
Throws:
IllegalAccessException - if you could not normally access this field (i.e. it is not public)
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
NullPointerException - if o is null and this field requires an instance
See Also:
set(Object,Object)

toGenericString

public String toGenericString()

toString

public 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 interface Object
Returns:
the String representation of the Field
java.lang.reflect.Field - reflection of Java fields Copyright (C) 1998, 2001, 2005, 2006 Free Software Foundation, Inc. This file is part of GNU Classpath. GNU Classpath is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. GNU Classpath is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU Classpath; see the file COPYING. If not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. Linking this library statically or dynamically with other modules is making a combined work based on this library. Thus, the terms and conditions of the GNU General Public License cover the whole combination. As a special exception, the copyright holders of this library give you permission to link this library with independent modules to produce an executable, regardless of the license terms of these independent modules, and to copy and distribute the resulting executable under terms of your choice, provided that you also meet, for each linked independent module, the terms and conditions of the license of that module. An independent module is a module which is not derived from or based on this library. If you modify this library, you may extend this exception to your version of the library, but you are not obligated to do so. If you do not wish to do so, delete this exception statement from your version.

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