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135 lines
4.5 KiB
135 lines
4.5 KiB
// kelondroMergeIterator.java
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// --------------------------
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// part of The Kelondro Database
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// (C) by Michael Peter Christen; mc@anomic.de
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// first published on http://www.anomic.de
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// Frankfurt, Germany, 2005
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// last major change: 08.05.2005
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//
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// This program is free software; you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation; either version 2 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program; if not, write to the Free Software
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// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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//
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// Using this software in any meaning (reading, learning, copying, compiling,
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// running) means that you agree that the Author(s) is (are) not responsible
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// for cost, loss of data or any harm that may be caused directly or indirectly
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// by usage of this softare or this documentation. The usage of this software
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// is on your own risk. The installation and usage (starting/running) of this
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// software may allow other people or application to access your computer and
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// any attached devices and is highly dependent on the configuration of the
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// software which must be done by the user of the software; the author(s) is
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// (are) also not responsible for proper configuration and usage of the
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// software, even if provoked by documentation provided together with
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// the software.
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//
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// Any changes to this file according to the GPL as documented in the file
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// gpl.txt aside this file in the shipment you received can be done to the
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// lines that follows this copyright notice here, but changes must not be
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// done inside the copyright notive above. A re-distribution must contain
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// the intact and unchanged copyright notice.
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// Contributions and changes to the program code must be marked as such.
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package de.anomic.kelondro;
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import java.util.Iterator;
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import java.util.Comparator;
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import java.util.Set;
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public class kelondroMergeIterator implements Iterator {
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Comparator comp;
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Iterator a, b;
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String na, nb;
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boolean up;
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public kelondroMergeIterator(Iterator a, Iterator b, boolean up) {
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// this works currently only for String-type key iterations
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this.a = a;
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this.b = b;
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this.up = up;
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this.comp = kelondroMSetTools.fastStringComparator(up);
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nexta();
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nextb();
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}
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public void finalize() {
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// call finalizer of embedded objects
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a = null;
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b = null;
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na = null;
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nb = null;
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comp = null;
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}
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private void nexta() {
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if (a.hasNext()) na = (String) a.next(); else na = null;
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}
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private void nextb() {
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if (b.hasNext()) nb = (String) b.next(); else nb = null;
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}
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public boolean hasNext() {
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return (na != null) || (nb != null);
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}
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public Object next() {
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String s;
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if (na == null) {
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s = nb;
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nextb();
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return s;
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}
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if (nb == null) {
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s = na;
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nexta();
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return s;
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}
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// compare the strings
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int c = comp.compare(na, nb);
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if (c == 0) {
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s = na;
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nexta();
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nextb();
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return s;
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} else if ((up) && (c < 0)) {
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s = na;
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nexta();
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return s;
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} else {
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s = nb;
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nextb();
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return s;
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}
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}
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public void remove() {
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throw new java.lang.UnsupportedOperationException("merge does not support remove");
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}
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public static Iterator cascade(Set /*of*/ iterators, boolean up) {
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// this extends the ability to combine two iterators
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// to the abiliy of combining a set of iterators
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if (iterators == null) return null;
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if (iterators.size() == 0) return null;
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return cascade(iterators.iterator(), up);
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}
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private static Iterator cascade(Iterator /*of*/ iiterators, boolean up) {
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if (iiterators == null) return null;
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if (!(iiterators.hasNext())) return null;
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Iterator one = (Iterator) iiterators.next();
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if (!(iiterators.hasNext())) return one;
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return new kelondroMergeIterator(one, cascade(iiterators, up), up);
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}
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}
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