JavaTM 2 Platform
Std. Ed. v1.4.2

java.lang.reflect
Class Field

java.lang.Object
  extended byjava.lang.reflect.AccessibleObject
      extended byjava.lang.reflect.Field
All Implemented Interfaces:
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.
 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.
 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.
 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.
 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 toString()
          Returns a string describing this Field.
 
Methods inherited from class java.lang.reflect.AccessibleObject
isAccessible, 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

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

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.

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.

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)

JavaTM 2 Platform
Std. Ed. v1.4.2

Submit a bug or feature
For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

Copyright 2003 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.


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