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AdapterRegistry.java | - | - | - | - |
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// Copyright 2004, 2005 The Apache Software Foundation
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package org.apache.hivemind.lib.util;
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/**
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* An implementation of the <b>adapter </b> pattern. The adapter pattern allows new functionality to
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* be assigned to an existing class. As implemented here, this is a smart lookup between a
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* particular class (the class to be adapted, called the <em>subject class</em>) and some object
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* instance that can provide the extra functionality (called the <em>adapter</em>). The
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* implementation of the adapter is not relevant to the adapterRegistry class.
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* <p>
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* adapters are registered before they can be used; the registration maps a particular class to an
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* adapter instance. The adapter instance will be used when the subject class matches the registered
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* class, or the subject class inherits from the registered class.
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* <p>
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* This means that a search must be made that walks the inheritance tree (upwards from the subject
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* class) to find a registered mapping.
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* <p>
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* In addition, adapters can be registered against <em>interfaces</em>. Searching of interfaces
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* occurs after searching of classes. The exact order is:
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* <ul>
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* <li>Search for the subject class, then each super-class of the subject class (excluding
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* java.lang.Object)
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* <li>Search interfaces, starting with interfaces implemented by the subject class, continuing
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* with interfaces implemented by the super-classes, then interfaces extended by earlier interfaces
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* (the exact order is a bit fuzzy)
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* <li>Search for a match for java.lang.Object, if any
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* </ul>
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* <p>
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* The first match terminates the search.
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* <p>
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* The AdapterRegistry caches the results of search; a subsequent search for the same subject class
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* will be resolved immediately.
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* <p>
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* AdapterRegistry does a minor tweak of the "natural" inheritance. Normally, the parent class of an
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* object array (i.e., <code>Foo[]</code>) is simply <code>Object</code>, even though you may
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* assign <code>Foo[]</code> to a variable of type <code>Object[]</code>. AdapterRegistry
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* "fixes" this by searching for <code>Object[]</code> as if it was the superclass of any object
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* array. This means that the search path for <code>Foo[]</code> is <code>Foo[]</code>,
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* <code>Object[]</code>, then a couple of interfaces {@link java.lang.Cloneable},
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* {@link java.io.Serializable}, etc. that are implicitily implemented by arrays), and then,
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* finally, <code>Object</code>
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* <p>
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* This tweak doesn't apply to arrays of primitives, since such arrays may <em>not</em> be
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* assigned to <code>Object[]</code>.
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*
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* @author Howard M. Lewis Ship
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* @see org.apache.hivemind.lib.util.AdapterRegistryImpl
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* @since 1.1
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*/
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public interface AdapterRegistry |
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{ |
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/**
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* Registers an adapter for a registration class.
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*
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* @throws IllegalArgumentException
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* if an adapter has already been registered for the given class.
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*/
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public void register(Class registrationClass, Object adapter); |
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/**
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* Gets the adapter for the specified subjectClass.
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*
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* @throws IllegalArgumentException
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* if no adapter could be found.
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*/
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public Object getAdapter(Class subjectClass);
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} |
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