001: /*
002: * $Id: LimitingRowIterator.java,v 1.10 2005/03/25 23:23:11 ahimanikya Exp $
003: * =======================================================================
004: * Copyright (c) 2002-2005 Axion Development Team. All rights reserved.
005: *
006: * Redistribution and use in source and binary forms, with or without
007: * modification, are permitted provided that the following conditions
008: * are met:
009: *
010: * 1. Redistributions of source code must retain the above
011: * copyright notice, this list of conditions and the following
012: * disclaimer.
013: *
014: * 2. Redistributions in binary form must reproduce the above copyright
015: * notice, this list of conditions and the following disclaimer in
016: * the documentation and/or other materials provided with the
017: * distribution.
018: *
019: * 3. The names "Tigris", "Axion", nor the names of its contributors may
020: * not be used to endorse or promote products derived from this
021: * software without specific prior written permission.
022: *
023: * 4. Products derived from this software may not be called "Axion", nor
024: * may "Tigris" or "Axion" appear in their names without specific prior
025: * written permission.
026: *
027: * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
028: * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
029: * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
030: * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
031: * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
032: * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
033: * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
034: * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
035: * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
036: * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
037: * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
038: * =======================================================================
039: */
040:
041: package org.axiondb.engine.rowiterators;
042:
043: import org.axiondb.AxionException;
044: import org.axiondb.Literal;
045: import org.axiondb.RowIterator;
046:
047: /**
048: * {@link RowIterator}implementing LIMIT and OFFSET.
049: *
050: * @version $Revision: 1.10 $ $Date: 2005/03/25 23:23:11 $
051: * @author Rodney Waldhoff
052: * @author Ahimanikya Satapathy
053: */
054: public class LimitingRowIterator extends AbstractFilteringRowIterator {
055:
056: public LimitingRowIterator(RowIterator iter, Literal limit,
057: Literal offset) {
058: super (iter);
059: _limit = limit;
060: _offset = offset;
061: }
062:
063: public String toString() {
064: return "Limiting(" + _limit + ")";
065: }
066:
067: protected boolean determineNextRow() throws AxionException {
068: // if _previousRowSet is true, then we've walked back in the delegate list
069: // so skip one matching row
070: if (isPreviousAvailable()) {
071: clearPreviousRow();
072: getDelegate().next();
073: clearNextRow();
074: }
075:
076: // skip to offset if needed and possible
077: while (!overOffset(getDelegate().nextIndex())) {
078: if (getDelegate().hasNext()) {
079: getDelegate().next();
080: } else {
081: return false;
082: }
083: }
084:
085: // check within my limit
086: if (underLimit(nextIndex()) && getDelegate().hasNext()) {
087: setNext(getDelegate().next());
088: return true;
089: }
090: return false;
091: }
092:
093: protected boolean determinePreviousRow() throws AxionException {
094: // if _nextRowSet is true, then we've walked forward in the delegate list
095: // so skip one matching row
096: if (isNextAvailable()) {
097: clearNextRow();
098: determinePreviousRow();
099: clearPreviousRow();
100: }
101:
102: if (overOffset(getDelegate().previousIndex())
103: && getDelegate().hasPrevious()) {
104: setPrevious(getDelegate().previous());
105: return true;
106: }
107: return false;
108: }
109:
110: private boolean overOffset(int index) throws AxionException {
111: return null == _offset
112: || (index >= ((Number) (_offset.evaluate(null)))
113: .intValue());
114: }
115:
116: private boolean underLimit(int index) throws AxionException {
117: return null == _limit
118: || (index < ((Number) (_limit.evaluate(null)))
119: .intValue());
120: }
121:
122: private Literal _limit;
123: private Literal _offset;
124: }
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