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git-svn-id: https://svn.berlios.de/svnroot/repos/yacy/trunk@6918 6c8d7289-2bf4-0310-a012-ef5d649a1542
83 lines
2.4 KiB
Java
83 lines
2.4 KiB
Java
// LookAheadIterator.java
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// (C) 2010 by Michael Peter Christen; mc@yacy.net, Frankfurt a. M., Germany
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// first published 04.02.2010 on http://yacy.net
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//
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// This is a part of YaCy, a peer-to-peer based web search engine
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//
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// $LastChangedDate: 2006-04-02 22:40:07 +0200 (So, 02 Apr 2006) $
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// $LastChangedRevision: 6539 $
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// $LastChangedBy: low012 $
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//
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// LICENSE
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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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package net.yacy.kelondro.util;
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import java.util.Iterator;
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/**
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* convenience class for iterator implementations that naturally terminate
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* when the next() method would return null. This is usually implemented using
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* a next0() method and a wrapper for next() and hasNext() that evaluates the
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* latest return value of next0()
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* To use this class just implement the next0() method
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*/
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public abstract class LookAheadIterator<A> implements Iterator<A>, Iterable<A> {
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private boolean fresh = true;
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private A next = null;
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public LookAheadIterator() {
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}
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public Iterator<A> iterator() {
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return this;
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}
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/**
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* the internal next-method
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* @return a value of type A if available or null if no more value are available
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*/
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protected abstract A next0() ;
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private final void checkInit() {
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if (fresh) {
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next = next0();
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fresh = false;
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}
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}
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public final boolean hasNext() {
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checkInit();
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return next != null;
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}
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public final A next() {
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checkInit();
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A n = next;
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next = next0();
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return n;
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}
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/**
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* a remove is not possible with this implementation
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*/
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public final void remove() {
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throw new UnsupportedOperationException();
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}
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}
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