/*
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* CDDL HEADER START
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*
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* The contents of this file are subject to the terms of the
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* Common Development and Distribution License, Version 1.0 only
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* (the "License"). You may not use this file except in compliance
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* with the License.
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*
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* You can obtain a copy of the license at
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* trunk/opends/resource/legal-notices/OpenDS.LICENSE
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* or https://OpenDS.dev.java.net/OpenDS.LICENSE.
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* See the License for the specific language governing permissions
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* and limitations under the License.
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*
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* When distributing Covered Code, include this CDDL HEADER in each
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* file and include the License file at
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* trunk/opends/resource/legal-notices/OpenDS.LICENSE. If applicable,
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* add the following below this CDDL HEADER, with the fields enclosed
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* by brackets "[]" replaced with your own identifying information:
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* Portions Copyright [yyyy] [name of copyright owner]
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*
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* CDDL HEADER END
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*
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*
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* Copyright 2009 Sun Microsystems, Inc.
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*/
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package org.opends.sdk.schema;
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/**
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* This class provides schema-local variables. These variables differ
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* from their normal counterparts in that each schema has its own
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* independently initialized copy of the variable. {@code SchemaLocal}
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* instances are typically private static fields in classes that wish to
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* associate state with a schema (e.g., a schema dependent cache).
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*
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* @param <T>
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* The type of the schema-local variable.
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*/
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public class SchemaLocal<T>
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{
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/**
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* Creates a schema-local variable.
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*/
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public SchemaLocal()
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{
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// Nothing to do.
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}
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/**
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* Returns the value in the provided schema's copy of this
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* schema-local variable. If the variable has no value associated with
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* the schema, it is first initialized to the value returned by an
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* invocation of the {@link #initialValue} method.
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*
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* @param schema
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* The schema whose copy of the schema-local variable is
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* being requested.
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* @return The schema-local value.
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*/
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public final T get(Schema schema)
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{
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// Schema calls back to initialValue() if this is the first time.
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return schema.getAttachment(this);
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}
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/**
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* Removes the provided schema's value for this schema-local variable.
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* If this schema-local variable is subsequently read, its value will
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* be reinitialized by invoking its {@link #initialValue} method,
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* unless its value is set in the interim. This may result in multiple
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* invocations of the {@link #initialValue} method.
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*
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* @param schema
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* The schema whose copy of the schema-local variable is
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* being removed.
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*/
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public final void remove(Schema schema)
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{
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schema.removeAttachment(this);
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}
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/**
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* Sets the provided schema's copy of this schema-local variable to
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* the specified value.
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*
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* @param schema
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* The schema whose copy of the schema-local variable is
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* being set.
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* @param value
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* The schema-local value.
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*/
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public final void set(Schema schema, T value)
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{
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schema.setAttachment(this, value);
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}
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/**
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* Returns the provided schema's "initial value" for this schema-local
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* variable. This method will be invoked the first time the variable
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* is accessed with the {@link #get} method for each schema, unless
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* the {@link #set} method has been previously invoked, in which case
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* the {@link #initialValue} method will not be invoked.
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* <p>
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* Normally, this method is invoked at most once per schema, but it
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* may be invoked again in case of subsequent invocations of
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* {@link #remove} followed by {@link #get}. This implementation
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* simply returns {@code null}; if the programmer desires schema-local
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* variables to have an initial value other than {@code null}, {@code
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* SchemaLocal} must be subclassed, and this method overridden.
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* Typically, an anonymous inner class will be used.
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*
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* @return The initial value for this schema-local.
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*/
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protected T initialValue()
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{
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// Default implementation.
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return null;
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}
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}
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