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/**
* LookAheadIterator
* Copyright 2010 by Michael Peter Christen; mc@yacy.net, Frankfurt a. M., Germany
* First published 04.02.2010 on http://yacy.net
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program in the file lgpl21.txt
* If not, see <http://www.gnu.org/licenses/>.
*/
package net.yacy.cora.util;
import java.util.Iterator;
/**
* convenience class for iterator implementations that naturally terminate
* when the next() method would return null. This is usually implemented using
* a next0() method and a wrapper for next() and hasNext() that evaluates the
* latest return value of next0()
* To use this class just implement the next0() method
*/
public abstract class LookAheadIterator<A> implements Iterator<A>, Iterable<A> {
private boolean fresh = true;
private A next = null;
public LookAheadIterator() {
}
@Override
public final Iterator<A> iterator() {
return this;
}
/**
* the internal next-method
* @return a value of type A if available or null if no more value are available
*/
protected abstract A next0() ;
private final void checkInit() {
if (this.fresh) {
this.next = next0();
this.fresh = false;
}
}
@Override
public final boolean hasNext() {
checkInit();
return this.next != null;
}
@Override
public final A next() {
checkInit();
final A n = this.next;
this.next = next0();
return n;
}
/**
* a remove is not possible with this implementation
*/
@Override
public final void remove() {
throw new UnsupportedOperationException();
}
}
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