wiki-export/wiki-content/DevFaqLookupCookie.xml

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  <page>
    <title>DevFaqLookupCookie</title>
    <id>7372</id>
    <revision>
      <id>26156</id>
      <timestamp>2009-11-06T15:51:49Z</timestamp>
      <contributor>
        <username>Admin</username>
        <id>1</id>
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      <text xml:space="preserve">__NOTOC__
===What is the difference between getCookie(Class), SharedClassObject.get(Class) and Lookup.lookup(Class)?===

All of these are really historical variations on the same theme.  In all cases, you pass a &lt;tt&gt;Class&lt;/tt&gt; object and get back null or an instance of that class.  You can see the progression in genericness:

&lt;tt&gt;SharedClassObject&lt;/tt&gt; is the oldest version of the Lookup pattern in NetBeans APIs, dating to circa 1997 (because of various performance issues, eventually all usages of &lt;tt&gt;SharedClassObject&lt;/tt&gt; should be deprecated and removed from the APIs).  You'll see that form used in &lt;tt&gt;SystemOption&lt;/tt&gt; for storing settings, and most of the singleton Action objects in the actions API.  All objects returned by it will be instances of &lt;tt&gt;SharedClassObject&lt;/tt&gt;.

&lt;tt&gt;getCookie()&lt;/tt&gt; (circa 1999) is specific to [[DevFaqWhatIsANode| Node]]s and [[DevFaqDataObject| DataObject]]s.  It uses the same pattern, but all objects returned by it will implement the empty &lt;tt&gt;Node.Cookie&lt;/tt&gt; marker interface.

The down-side to both of the above is that they specify the return type.  In the case of &lt;tt&gt;Node.Cookie&lt;/tt&gt;, in practice, this meant that anything that might possibly need to be provided by a &lt;tt&gt;DataObject&lt;/tt&gt; or &lt;tt&gt;Node&lt;/tt&gt; needed to implement this silly marker interface, forcing it to have a dependency on the Nodes API, or a wrapper Cookie class had to be created to provide the underlying object, which just added useless classes and noise.

[[DevFaqLookup| Lookup]] is the most modern and generic version of this pattern, and probably the final one.  It offers two advantages:
# Its return type is &lt;tt&gt;java.lang.Object&lt;/tt&gt;, so it can be used directly with anything
# Having objects ''own'' a lookup rather than directly providing a &lt;tt&gt;lookup(Class c)&lt;/tt&gt; method makes it easier to replace or proxy the Lookup of some object</text>
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