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The Java Data Objects API (JDO) : a standard interface-based Java model abstraction of persistence, developed by the JCP.
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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *     http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software 
 * distributed under the License is distributed on an "AS IS" BASIS, 
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
 * See the License for the specific language governing permissions and 
 * limitations under the License.
 */

/*
 * Extent.java
 *
 */
package javax.jdo;

import java.lang.Iterable;
import java.util.Iterator;

/**
 * Instances of the Extent class represent the entire collection of instances in the data store of the candidate class or interface
 * possibly including its subclasses or subinterfaces.
 * The Extent instance has two possible uses:
 * 

 * to iterate all instances of a particular class or interface
 * 
to execute a Query in the data store over all instances
 * of a particular class or interface
 * 
 */
public interface Extent extends AutoCloseable, Iterable {

    /**
     * Returns an iterator over all the instances in the Extent.
     * The behaviour of the returned iterator might depend on the setting of the ignoreCache flag in the owning PersistenceManager.
     * @return an iterator over all instances in the Extent
     */
    Iterator iterator();

    /**
     * Returns whether this Extent was defined to contain subclasses.
     * @return true if this Extent was defined to contain instances that are of a subclass type.
     */    
    boolean hasSubclasses();

    /**
     * An Extent contains all instances of a particular class or interface in the data
     * store; this method returns the Class of the instances represented by this Extent.
     * @return the Class of instances of this Extent.
     */
    Class getCandidateClass();

    /**
     * An Extent is managed by a PersistenceManager;
     * this method gives access to the owning PersistenceManager.
     * @return the owning PersistenceManager
     */
    PersistenceManager getPersistenceManager();

    /**
     * Close all Iterators associated with this Extent instance.
     * Iterators closed by this method will return false to hasNext() and will throw
     * NoSuchElementException on next().
     * The Extent instance can still be used as a parameter of Query.setExtent, and to get an Iterator.
     */    
    void closeAll();

    /**
     * Close an Iterator associated with this Extent instance.
     * Iterators closed by this method will return false to hasNext() and will throw NoSuchElementException 
     * on next(). The Extent instance can still be used as a parameter of Query.setExtent, and to get an Iterator.
     * @param it an Iterator obtained by the method iterator() on this Extent instance.
     */
    void close(Iterator it);

    /**
     * Don't use this method directly; use closeAll() instead. It is intended for use with try-with-resources.
     * @throws Exception if this resource cannot be closed
     */
    void close() throws Exception;

    /**
     * Get the fetch plan associated with this Extent.
     * @return the fetch plan
     * @since 2.0
     */
    FetchPlan getFetchPlan();
}