factory.html

Geotools是一个开源的Java GIS工具包,可利用它来开发符合标准的地理信息系统。Geotools提供了OGC(Open Geospatial Consortium)规范的一个实现来作为他们的

<DD>Map of  hints (maybe <A HREF="http://java.sun.com/j2se/1.4/docs/api/java/util/Collections.html#unmodifiableMap(java.util.Map)" title="class or interface in java.util">unmodifiable</A>)
 used by this factory to customize its use. This map is <strong>not</strong> guaranteed
 to contains all the hints supplied by the user; it may be only a subset. Consequently,
 hints provided here are usually not suitable for creating new factories, unless the
 implementation make some additional garantees (e.g.
 <A HREF="../../../org/geotools/factory/FactoryUsingVolatileDependencies.html" title="class in org.geotools.factory"><CODE>FactoryUsingVolatileDependencies</CODE></A>).
 <p>
 The primary purpose of this method is to determine if an <strong>existing</strong>
 factory instance can be reused for a set of user-supplied hints. This method is invoked by
 <A HREF="../../../org/geotools/factory/FactoryRegistry.html" title="class in org.geotools.factory"><CODE>FactoryRegistry</CODE></A> in order to compare this factory's hints against user's hints.
 This is dependency introspection only;  <strong>never</strong>
 invokes this method for creating new factories.
 <p>
 Keys are usually static constants from the <A HREF="../../../org/geotools/factory/Hints.html" title="class in org.geotools.factory"><CODE>Hints</CODE></A> class, while values are
 instances of some key-dependent class. The <A HREF="http://java.sun.com/j2se/1.4/docs/api/java/util/Map.html#keySet()" title="class or interface in java.util">key set</A> must contains
 at least all hints impacting functionality. While the key set may contains all hints
 supplied by the user, it is recommended to limit the set to only the hints used by this
 particular factory instance. A minimal set will helps <A HREF="../../../org/geotools/factory/FactoryRegistry.html" title="class in org.geotools.factory"><CODE>FactoryRegistry</CODE></A> to compares
 only hints that matter and avoid the creation of unnecessary instances of this factory.
 <p>
 The hint values may be different than the one supplied by the user. If a user supplied a
 hint as a <A HREF="http://java.sun.com/j2se/1.4/docs/api/java/lang/Class.html" title="class or interface in java.lang"><CODE>Class</CODE></A> object, this method shall replace it by the actual instance used, if
 possible.
 <p>
 Implementations of this method are usually quite simple. For example if a
 datum authority factory
 uses an ordinary datum factory,
 its method could be implemented as below (note that we should not check if the datum
 factory is null, since key with null value is the expected behaviour in this case).
 Example:

 <pre><code>
 Map hints = new HashMap();
 hints.put(<A HREF="../../../org/geotools/factory/Hints.html#DATUM_FACTORY">Hints.DATUM_FACTORY</A>, datumFactory);
 return hints;
 </code></pre>
<P>
<DD><DL>

<DT><B>Returns:</B><DD>The map of hints, or an <A HREF="http://java.sun.com/j2se/1.4/docs/api/java/util/Collections.html#EMPTY_MAP" title="class or interface in java.util">empty map</A>
         if none.</DL>
</DD>
</DL>
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