001/* 002 * Licensed to the Apache Software Foundation (ASF) under one 003 * or more contributor license agreements. See the NOTICE file 004 * distributed with this work for additional information 005 * regarding copyright ownership. The ASF licenses this file 006 * to you under the Apache License, Version 2.0 (the 007 * "License"); you may not use this file except in compliance 008 * with the License. You may obtain a copy of the License at 009 * 010 * http://www.apache.org/licenses/LICENSE-2.0 011 * 012 * Unless required by applicable law or agreed to in writing, 013 * software distributed under the License is distributed on an 014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY 015 * KIND, either express or implied. See the License for the 016 * specific language governing permissions and limitations 017 * under the License. 018 * 019 */ 020package org.apache.directory.mavibot.btree; 021 022 023import java.io.IOException; 024 025import org.apache.directory.mavibot.btree.exception.EndOfFileExceededException; 026 027 028/** 029 * A Cursor is used to fetch elements in a BTree and is returned by the 030 * @see BTree#browse method. The cursor <strng>must</strong> be closed 031 * when the user is done with it. 032 * <p> 033 * 034 * @param <K> The type for the Key 035 * 036 * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a> 037 */ 038public interface Cursor<K> 039{ 040 /** Static value for the beforeFrst and afterLast positions */ 041 int BEFORE_FIRST = -1; 042 int AFTER_LAST = -2; 043 044 045 /** 046 * Tells if the cursor can return a next element 047 * @return true if there are some more elements 048 * @throws IOException 049 * @throws EndOfFileExceededException 050 */ 051 boolean hasNext() throws EndOfFileExceededException, IOException; 052 053 054 /** 055 * Tells if the cursor can return a previous element 056 * @return true if there are some more elements 057 * @throws IOException 058 * @throws EndOfFileExceededException 059 */ 060 boolean hasPrev() throws EndOfFileExceededException, IOException; 061 062 063 /** 064 * Closes the cursor, thus releases the associated transaction 065 */ 066 void close(); 067 068 069 /** 070 * moves the cursor to the same position that was given at the time of instantiating the cursor. 071 * 072 * For example, if the cursor was created using browse() method, then beforeFirst() will 073 * place the cursor before the 0th position. 074 * 075 * If the cursor was created using browseFrom(K), then calling beforeFirst() will reset the position 076 * to the just before the position where K is present. 077 */ 078 void beforeFirst() throws IOException; 079 080 081 /** 082 * Places the cursor at the end of the last position 083 * 084 * @throws IOException 085 */ 086 void afterLast() throws IOException; 087}