Field (Java 2 Platform SE v1.4.1_"07")

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JavaTM 2 Platform
Std. Ed. v1.4.1_"07"

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## java.lang.reflect
Class Field

    java.lang.Object
      |
      +--java.lang.reflect.AccessibleObject
            |
            +--java.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)`

Overview | Package | Class | Use | Tree | Deprecated | Index | Help

JavaTM 2 Platform
Std. Ed. v1.4.1_"07"

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