Eclipse Plug-in Developer Guide (Galileo) - HandleObject (Eclipse Platform API Specification)

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Eclipse Platform
Release 3.5

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org.eclipse.core.commands.common
Class HandleObject


java.lang.Object
  

org.eclipse.core.commands.common.EventManager
      
org.eclipse.core.commands.common.HandleObject

All Implemented Interfaces:: IIdentifiable

Direct Known Subclasses:: NamedHandleObject, ParameterType

public abstract class HandleObject
extends EventManager
implements IIdentifiable
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.

Since:: 3.1

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

defined

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.

id

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.

string

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

HandleObject

protected HandleObject(
String id)

Constructs a new instance of HandleObject.

Parameters:: id - The id of this handle; must not be null.

Method Detail

equals

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.

Overrides:: equals in class Object

Parameters:: object - The object with which to compare; may be null.
Returns:: true if the objects are equal; false otherwise.

getId

public final 
String getId()

Description copied from interface: IIdentifiable

Returns the identifier for this object.

Specified by:: getId in interface IIdentifiable

Returns:: The identifier; never null.

hashCode

public final int hashCode()

Computes the hash code for this object based on the id.

Overrides:: hashCode in class Object

Returns:: The hash code for this object.

isDefined

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.

Returns:: true if this object is defined; false otherwise.

toString

public abstract 
String toString()

The string representation of this object -- for debugging purposes only. This string should not be shown to an end user.

Overrides:: toString in class Object

Returns:: The string representation; never null.

undefine

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.