/*******************************************************************************
* Copyright 2010 Cees De Groot, Alex Boisvert, Jan Kotek
*
* Licensed 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.
******************************************************************************/
package de.mxro.thrd.jdbm2V22.recman;
import java.io.IOException;
/**
* This class provides a cursor that can follow lists of pages
* bi-directionally.
*/
final class PageCursor {
PageManager pageman;
long current;
short type;
/**
* Constructs a page cursor that starts at the indicated block.
*/
PageCursor(PageManager pageman, long current) {
this.pageman = pageman;
this.current = current;
}
/**
* Constructs a page cursor that starts at the first block
* of the indicated list.
*/
PageCursor(PageManager pageman, short type) throws IOException {
this.pageman = pageman;
this.type = type;
}
/**
* Returns the current value of the cursor.
*/
long getCurrent() throws IOException {
return current;
}
/**
* Returns the next value of the cursor
*/
long next() throws IOException {
if (current == 0)
current = pageman.getFirst(type);
else
current = pageman.getNext(current);
return current;
}
/**
* Returns the previous value of the cursor
*/
long prev() throws IOException {
current = pageman.getPrev(current);
return current;
}
}