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Java > Open Source Codes > com > sleepycat > persist > ValueAdapter


1 /*-
2  * See the file LICENSE for redistribution information.
3  *
4  * Copyright (c) 2002,2006 Oracle. All rights reserved.
5  *
6  * $Id: ValueAdapter.java,v 1.5 2006/10/30 21:14:30 bostic Exp $
7  */
8
9 package com.sleepycat.persist;
10
11 import com.sleepycat.je.DatabaseEntry;
12
13 /**
14  * An adapter that translates between database entries (key, primary key, data)
15  * and a "value", which may be either the key, primary key, or entity. This
16  * interface is used to implement a generic index and cursor (BasicIndex and
17  * BasicCursor). If we didn't use this approach, we would need separate index
18  * and cursor implementations for each type of value that can be returned. In
19  * other words, this interface is used to reduce class explosion.
20  *
21  * @author Mark Hayes
22  */
23 interface ValueAdapter<V> {
24
25     /**
26      * Creates a DatabaseEntry for the key or returns null if the key is not
27      * needed.
28      */
29     DatabaseEntry initKey();
30
31     /**
32      * Creates a DatabaseEntry for the primary key or returns null if the
33      * primary key is not needed.
34      */
35     DatabaseEntry initPKey();
36
37     /**
38      * Creates a DatabaseEntry for the data or returns null if the data is not
39      * needed. BasicIndex.NO_RETURN_ENTRY may be returned if the data argument
40      * is required but we don't need it.
41      */
42     DatabaseEntry initData();
43
44     /**
45      * Sets the data array of the given entries to null, based on knowledge of
46      * which entries are non-null and are not NO_RETURN_ENTRY.
47      */
48     void clearEntries(DatabaseEntry key,
49                       DatabaseEntry pkey,
50                       DatabaseEntry data);
51
52     /**
53      * Returns the appropriate "value" (key, primary key, or entity) using the
54      * appropriate bindings for that purpose.
55      */
56     V entryToValue(DatabaseEntry key,
57                    DatabaseEntry pkey,
58                    DatabaseEntry data);
59
60     /**
61      * Converts an entity value to a data entry using an entity binding, or
62      * throws UnsupportedOperationException if this is not appropriate. Called
63      * by BasicCursor.update.
64      */
65     void valueToData(V value, DatabaseEntry data);
66 }
67
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