com.webobjects.foundation
Class NSKeyValueCoding.Null

java.lang.Object
  com.webobjects.foundation.NSKeyValueCoding.Null

All Implemented Interfaces:

NSCoding, Serializable, Cloneable

Enclosing interface:

NSKeyValueCoding

public static final class NSKeyValueCoding.Null
extends Object
implements Serializable, Cloneable, NSCoding

NSKeyValueCoding.Null is a final class that defines a unique object used to represent null values in collection objects, such as NSArrays, which do not allow null values.

For instance, Enterprise Objects Framework uses NSKeyValueCoding.Null to represent null values from database rows in its database level snapshots (NSDictionary objects). However, Enterprise Objects Framework automatically translates NSKeyValueCoding.Null to null in enterprise objects, so you should rarely need to write code that accounts for this class.

Whenever null is represented by NSKeyValueCoding.Null, it should be represented with the instance stored in the NSKeyValueCoding constant, NullValue. You can safely use this instance with the == operator to test for the presence of a null value:

          <blockquote>
           if (value == NSKeyValueCoding.NullValue){
              //......
           }
           </blockquote>
 

See Also:

NSKeyValueCoding.NullValue, Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from interface com.webobjects.foundation.NSCoding

NSCoding.Support

Method Summary

Class	classForCoder() Allows the receiver, before being encoded, to substitute a class other than its own in a coder.
Object	clone() Simply returns the shared instance of NSKeyValueCoding.Null stored in the constant NullValue.
static Object	decodeObject(NSCoder coder) Returns the shared instance of NSKeyValueCoding.Null stored in the NSKeyValueCoding constant NullValue.
void	encodeWithCoder(NSCoder coder) Encodes the receiver using coder.
String	toString()

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Method Detail

toString

public String toString()

Overrides:

toString in class Object

Returns:

a string representation of the receiver

clone

public Object clone()

Simply returns the shared instance of NSKeyValueCoding.Null stored in the constant NullValue.

Overrides:

clone in class Object

Returns:

this

See Also:

NSKeyValueCoding.NullValue

classForCoder

public Class classForCoder()

Description copied from interface: NSCoding

Allows the receiver, before being encoded, to substitute a class other than its own in a coder. For example, private subclasses can substitute the name of a public superclass when being encoded.

Specified by:

classForCoder in interface NSCoding

Returns:

the class a coder should record

decodeObject

public static Object decodeObject(NSCoder coder)

Returns the shared instance of NSKeyValueCoding.Null stored in the NSKeyValueCoding constant NullValue.

Parameters:

coder - instructs the object to encode and decode its instance variables

Returns:

the shared instance of NSKeyValueCoding

See Also:

NSKeyValueCoding.NullValue, NSCoding

encodeWithCoder

public void encodeWithCoder(NSCoder coder)

Description copied from interface: NSCoding

Encodes the receiver using coder. Object type information along with an object's data is stored.

Specified by:

encodeWithCoder in interface NSCoding

Parameters:

coder - an NSCoder object that will be used to encode object of classes that implement this interface

See Also:

NSCoder