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Eclipse Platform
Release 3.5

Class HandleObject

  extended by 

      extended by 
All Implemented Interfaces:
Direct Known Subclasses:
NamedHandleObject, ParameterType

public abstract class HandleObject
extends EventManager
implements IIdentifiable

An object that can exist in one of two states: defined and undefined. This is used by APIs that want to give a handle to an object, even though the object does not fully exist yet. This way, users can attach listeners to objects before they come into existence. It also protects the API from users that do not release references when they should.

To enforce good coding practice, all handle objects must implement equals and toString. Please use string to cache the result for toString once calculated.

All handle objects are referred to using a single identifier. This identifier is a instance of String. It is important that this identifier remain unique within whatever context that handle object is being used. For example, there should only ever be one instance of Command with a given identifier.


Field Summary
protected  boolean defined
          Whether this object is defined.
protected   String id
          The identifier for this object.
protected   String string
          The string representation of this object.
Constructor Summary
protected HandleObject ( String id)
          Constructs a new instance of HandleObject.
Method Summary
 boolean equals ( Object object)
          Tests whether this object is equal to another object.
  String getId ()
          Returns the identifier for this object.
 int hashCode ()
          Computes the hash code for this object based on the id.
 boolean isDefined ()
          Whether this instance is defined.
abstract   String toString ()
          The string representation of this object -- for debugging purposes only.
abstract  void undefine ()
          Makes this object becomes undefined.
Methods inherited from class org.eclipse.core.commands.common. EventManager
addListenerObject, clearListeners, getListeners, isListenerAttached, removeListenerObject
Methods inherited from class java.lang. Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail


protected transient boolean defined
Whether this object is defined. A defined object is one that has been fully initialized. By default, all objects start as undefined.


protected final 
String id
The identifier for this object. This identifier should be unique across all objects of the same type and should never change. This value will never be null.


protected transient 
String string
The string representation of this object. This string is for debugging purposes only, and is not meant to be displayed to the user. This value is computed lazily, and is cleared if one of its dependent values changes.

Constructor Detail


protected HandleObject(
String id)
Constructs a new instance of HandleObject.

id - The id of this handle; must not be null.
Method Detail


public boolean equals(
Object object)
Tests whether this object is equal to another object. A handle object is only equal to another handle object with the same id and the same class.

equals in class Object
object - The object with which to compare; may be null.
true if the objects are equal; false otherwise.


public final 
String getId()
Description copied from interface: IIdentifiable
Returns the identifier for this object.

Specified by:
getId in interface IIdentifiable
The identifier; never null.


public final int hashCode()
Computes the hash code for this object based on the id.

hashCode in class Object
The hash code for this object.


public final boolean isDefined()
Whether this instance is defined. A defined instance is one that has been fully initialized. This allows objects to effectively disappear even though other objects may still have references to them.

true if this object is defined; false otherwise.


public abstract 
String toString()
The string representation of this object -- for debugging purposes only. This string should not be shown to an end user.

toString in class Object
The string representation; never null.


public abstract void undefine()
Makes this object becomes undefined. This method should make any defined properties null. It should also send notification to any listeners that these properties have changed.

Eclipse Platform
Release 3.5

Guidelines for using Eclipse APIs.

Copyright (c) Eclipse contributors and others 2000, 2008. All rights reserved.

  Published under the terms of the Eclipse Public License Version 1.0 ("EPL") Design by Interspire