Documentation  › java.lang.reflect  › Field
 
 


  Field
  public final

  Inherits From:   AccessibleObject : Object
  Conforms To:   Member
  Declared In:   java.lang.reflect


Class Description
 
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.



Class Variables
 
None declared in this class.


Instance Variables
 
None declared in this class.


Constructors
 
None declared in this class.


Class Methods
 
None declared in this class.


Instance Methods
 
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.


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.


getBoolean
public boolean getBoolean( Object obj ) throws IllegalArgumentException, IllegalAccessException

Gets the value of a static or instance boolean field.


getByte
public byte getByte( Object obj ) throws IllegalArgumentException, IllegalAccessException

Gets the value of a static or instance byte field.


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.


getDeclaringClass
public Class getDeclaringClass( )

Returns the Class object representing the class or interface that declares the field represented by this Field 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.


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.


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.


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.


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.


getName
public String getName( )

Returns the name of the field represented by this Field 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.


getType
public Class getType( )

Returns a Class object that identifies the declared type for the field represented by this Field object.


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.


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.


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.


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.


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.


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.


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.


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.


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.


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.


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.



Known Subclasses
 
None.



 
 
  dydoc
  3/10/05