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Java(TM) 2 Platform, Standard Edition, v1.2.2 API Specification: Class Field - JDK 5 Documentation v1.2.2, Java 2 SDK 英文文档

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java.lang.reflect
Class Field

java.lang.Object
  |
  +--java.lang.reflect.AccessibleObject
        |
        +--java.lang.reflect.Field

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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(), java.lang.Class#getField(), Class.getDeclaredFields(), java.lang.Class#getDeclaredField()

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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 field as a boolean on the specified object.
byte	getByte(Object obj)           Gets the value of a field as a byte on the specified object.
char	getChar(Object obj)           Gets the value of a field as a char on the specified object.
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 field as a double on the specified object.
float	getFloat(Object obj)           Gets the value of a field as a float on the specified object.
int	getInt(Object obj)           Gets the value of a field as an int on the specified object.
long	getLong(Object obj)           Gets the value of a field as a long on the specified object.
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 field as a short on the specified object.
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

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getName

public String getName()

Returns the name of the field represented by this Field object.

Specified by:

getName in interface Member

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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

See Also:

Modifier

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getType

public Class getType()

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

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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

Tags copied from 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:

Boolean.hashCode(), Hashtable

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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

Tags copied from class: Object

Returns:

a hash code value for this object.

See Also:

Object.equals(java.lang.Object), Hashtable

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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

Tags copied from class: Object

Returns:

a string representation of the object.

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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.

Throws:

IllegalAccessException - if the underlying constructor 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.

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getBoolean

public boolean getBoolean(Object obj)
                   throws IllegalArgumentException,
                          IllegalAccessException

Gets the value of a field as a boolean on the specified object. This method is equivalent to ((Boolean)get(obj)).booleanValue(), except that an IllegalArgumentException is thrown if the field value cannot be converted to the type boolean by a widening conversion.

Throws:

IllegalAccessException - if the underlying constructor 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)

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getByte

public byte getByte(Object obj)
             throws IllegalArgumentException,
                    IllegalAccessException

Gets the value of a field as a byte on the specified object. This method is equivalent to ((Number)get(obj)).byteValue(), except that an IllegalArgumentException is thrown if the field value cannot be converted to the type byte by a widening conversion.

Throws:

IllegalAccessException - if the underlying constructor 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)

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getChar

public char getChar(Object obj)
             throws IllegalArgumentException,
                    IllegalAccessException

Gets the value of a field as a char on the specified object. This method is equivalent to ((Character)get(obj)).charValue(), except that an IllegalArgumentException is thrown if the field value cannot be converted to the type char by a widening conversion.

Throws:

IllegalAccessException - if the underlying constructor 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)

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getShort

public short getShort(Object obj)
               throws IllegalArgumentException,
                      IllegalAccessException

Gets the value of a field as a short on the specified object. This method is equivalent to ((Number)get(obj)).shortValue(), except that an IllegalArgumentException is thrown if the field value cannot be converted to the type short by a widening conversion.

Throws:

IllegalAccessException - if the underlying constructor 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)

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getInt

public int getInt(Object obj)
           throws IllegalArgumentException,
                  IllegalAccessException

Gets the value of a field as an int on the specified object. This method is equivalent to ((Number)get(obj)).intValue(), except that an IllegalArgumentException is thrown if the field value cannot be converted to the type int by a widening conversion.

Throws:

IllegalAccessException - if the underlying constructor 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)

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getLong

public long getLong(Object obj)
             throws IllegalArgumentException,
                    IllegalAccessException

Gets the value of a field as a long on the specified object. This method is equivalent to ((Number)get(obj)).longValue(), except that an IllegalArgumentException is thrown if the field value cannot be converted to the type long by a widening conversion.

Throws:

IllegalAccessException - if the underlying constructor 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)

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getFloat

public float getFloat(Object obj)
               throws IllegalArgumentException,
                      IllegalAccessException

Gets the value of a field as a float on the specified object. This method is equivalent to ((Number)get(obj)).floatValue(), except that an IllegalArgumentException is thrown if the field value cannot be converted to the type float by a widening conversion.

Throws:

IllegalAccessException - if the underlying constructor 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)

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getDouble

public double getDouble(Object obj)
                 throws IllegalArgumentException,
                        IllegalAccessException

Gets the value of a field as a double on the specified object. This method is equivalent to ((Number)get(obj)).doubleValue(), except that an IllegalArgumentException is thrown if the field value cannot be converted to the type double by a widening conversion.

Throws:

IllegalAccessException - if the underlying constructor 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)

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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.

Throws:

IllegalAccessException - if the underlying constructor 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.

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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.

Throws:

IllegalAccessException - if the underlying constructor 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)

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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.

Throws:

IllegalAccessException - if the underlying constructor 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)

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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.

Throws:

IllegalAccessException - if the underlying constructor 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)

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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.

Throws:

IllegalAccessException - if the underlying constructor 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)

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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.

Throws:

IllegalAccessException - if the underlying constructor 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)

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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.

Throws:

IllegalAccessException - if the underlying constructor 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)

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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.

Throws:

IllegalAccessException - if the underlying constructor 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)

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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.

Throws:

IllegalAccessException - if the underlying constructor 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)

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