java.lang.reflect

Class Field

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 {@link 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 getField getDeclaredField getFields getDeclaredFields

UNKNOWN: updated to 1.4

Method Summary
booleanequals(Object fld)
Compare two objects to see if they are semantically equivalent.
Objectget(Object obj)
Get the value of this Field.
<T extends Annotation> TgetAnnotation(Class<T> annoClass)
booleangetBoolean(Object obj)
Get the value of this boolean Field.
bytegetByte(Object obj)
Get the value of this byte Field.
chargetChar(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.
doublegetDouble(Object obj)
Get the value of this Field as a double.
floatgetFloat(Object obj)
Get the value of this Field as a float.
TypegetGenericType()
Return the generic type of the field.
intgetInt(Object obj)
Get the value of this Field as an int.
longgetLong(Object obj)
Get the value of this Field as a long.
intgetModifiers()
Gets the modifiers this field uses.
StringgetName()
Gets the name of this field.
shortgetShort(Object obj)
Get the value of this Field as a short.
Class<?>getType()
Gets the type of this field.
inthashCode()
Get the hash code for the Field.
booleanisEnumConstant()
Return true if this field represents an enum constant, false otherwise.
booleanisSynthetic()
Return true if this field is synthetic, false otherwise.
voidset(Object object, Object value)
Set the value of this Field.
voidsetBoolean(Object obj, boolean b)
Set this boolean Field.
voidsetByte(Object obj, byte b)
Set this byte Field.
voidsetChar(Object obj, char c)
Set this char Field.
voidsetDouble(Object obj, double d)
Set this double Field.
voidsetFloat(Object obj, float f)
Set this float Field.
voidsetInt(Object obj, int i)
Set this int Field.
voidsetLong(Object obj, long l)
Set this long Field.
voidsetShort(Object obj, short s)
Set this short Field.
StringtoGenericString()
StringtoString()
Get a String representation of the Field.

Method Detail

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.

Parameters: o the object to compare to

Returns: true if they are equal; false if not

get

public Object get(Object obj)
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: 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 ExceptionInInitializerError if accessing a static field triggered class initialization, which then failed

See Also: getBoolean getByte getChar getShort getInt getLong getFloat getDouble

getAnnotation

public <T extends Annotation> T getAnnotation(Class<T> annoClass)

getBoolean

public boolean getBoolean(Object obj)
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: 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 ExceptionInInitializerError if accessing a static field triggered class initialization, which then failed

See Also: get

getByte

public byte getByte(Object obj)
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: 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 ExceptionInInitializerError if accessing a static field triggered class initialization, which then failed

See Also: get

getChar

public char getChar(Object obj)
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 ExceptionInInitializerError if accessing a static field triggered class initialization, which then failed

See Also: get

getDeclaredAnnotations

public Annotation[] getDeclaredAnnotations()

getDeclaringClass

public Class<?> getDeclaringClass()
Gets the class that declared this field, or the class where this field is a non-inherited member.

Returns: the class that declared this member

getDouble

public double getDouble(Object obj)
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: 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 ExceptionInInitializerError if accessing a static field triggered class initialization, which then failed

See Also: get

getFloat

public float getFloat(Object obj)
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: 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 ExceptionInInitializerError if accessing a static field triggered class initialization, which then failed

See Also: get

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

getInt

public int getInt(Object obj)
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: 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 ExceptionInInitializerError if accessing a static field triggered class initialization, which then failed

See Also: get

getLong

public long getLong(Object obj)
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: 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 ExceptionInInitializerError if accessing a static field triggered class initialization, which then failed

See Also: get

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.

Returns: an integer representing the modifiers to this Member

See Also: Modifier

getName

public String getName()
Gets the name of this field.

Returns: the name of this field

getShort

public short getShort(Object obj)
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: 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 ExceptionInInitializerError if accessing a static field triggered class initialization, which then failed

See Also: get

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.

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.

Since: 1.5

set

public void set(Object object, Object value)
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: 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 ExceptionInInitializerError if accessing a static field triggered class initialization, which then failed

See Also: Field Field Field Field Field Field Field Field

setBoolean

public void setBoolean(Object obj, boolean b)
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: 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 ExceptionInInitializerError if accessing a static field triggered class initialization, which then failed

See Also: Field

setByte

public void setByte(Object obj, byte b)
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: 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 ExceptionInInitializerError if accessing a static field triggered class initialization, which then failed

See Also: Field

setChar

public void setChar(Object obj, char c)
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: 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 ExceptionInInitializerError if accessing a static field triggered class initialization, which then failed

See Also: Field

setDouble

public void setDouble(Object obj, double d)
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: 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 ExceptionInInitializerError if accessing a static field triggered class initialization, which then failed

See Also: Field

setFloat

public void setFloat(Object obj, float f)
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: 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 ExceptionInInitializerError if accessing a static field triggered class initialization, which then failed

See Also: Field

setInt

public void setInt(Object obj, int i)
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: 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 ExceptionInInitializerError if accessing a static field triggered class initialization, which then failed

See Also: Field

setLong

public void setLong(Object obj, long l)
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: 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 ExceptionInInitializerError if accessing a static field triggered class initialization, which then failed

See Also: Field

setShort

public void setShort(Object obj, short s)
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: 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 ExceptionInInitializerError if accessing a static field triggered class initialization, which then failed

See Also: Field

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

Returns: the String representation of the Field