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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.
 */

/*
 * Sequence.java
 *
 */
 
package javax.jdo.datastore;


/**
 *	Implementations of this interface can be used to obtain
 *	sequences. The behavior with regard to the transaction and
 *	rollover behavior are defined in the metadata.
 *
 *	@version 2.0
 *	@since 2.0
 */
public interface Sequence {

    /**
     * Returns the fully qualified name of the Sequence.
     * @return the name of the sequence
     */
    String getName ();

    /**
     * Returns the next sequence value as an Object. If the next
     * sequence value is not available, throw JDODataStoreException.
     * @return the next value
     */
    Object next ();

    /**
     * Provides a hint to the implementation that the application
     * will need additional sequence value objects in
     * short order. There is no externally visible behavior of this
     * method. It is used to potentially improve the efficiency of
     * the algorithm of obtaining additional sequence value objects.
     * @param additional the number of additional values to allocate
     */
    void allocate (int additional);

    /**
     * Returns the current sequence value object if it is
     * available. It is intended to return a sequence value object
     * previously used. If the current sequence value is not available,
     * throw JDODataStoreException.
     * @return the current value
     */
    Object current ();
    
    /** 
     * Returns the next sequence value as a long. If the next
     * sequence value is not available or is not numeric, throw
     * JDODataStoreException.
     * @return the next value
     */
    long nextValue();
    
    /** 
     * Returns the current sequence value as a long. If the current
     * sequence value is not available or is not numeric, throw
     * JDODataStoreException.
     * @return the current value
     */
    long currentValue();
}