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package de.lmu.ifi.dbs.elki.utilities.iterator;
/*
This file is part of ELKI:
Environment for Developing KDD-Applications Supported by Index-Structures
Copyright (C) 2012
Ludwig-Maximilians-Universität München
Lehr- und Forschungseinheit für Datenbanksysteme
ELKI Development Team
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program 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 Affero General Public License for more details.
You should have received a copy of the GNU Affero General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
import java.util.Iterator;
import de.lmu.ifi.dbs.elki.utilities.exceptions.AbortException;
/**
* Abstract class to build filtered views on Iterables.
*
* @author Erich Schubert
*
* @apiviz.stereotype decorator
* @apiviz.composedOf Iterator
*
* @param <IN> Input type
* @param <OUT> Output type
*/
public abstract class AbstractFilteredIterator<IN, OUT extends IN> implements Iterator<OUT> {
/**
* The iterator to use.
*/
Iterator<IN> itr = null;
/**
* The next object to return.
*/
OUT nextobj = null;
/**
* Constructor.
*/
public AbstractFilteredIterator() {
super();
}
/**
* Init the iterators
*/
protected void init() {
this.itr = getParentIterator();
if (this.itr == null) {
throw new AbortException("Filtered iterator has 'null' parent.");
}
}
/**
* Get an iterator for the actual data. Used in initialization.
*
* @return iterator
*/
abstract protected Iterator<IN> getParentIterator();
/**
* Test the filter predicate for a new object.
*
* @param nextobj Object to test
* @return cast object when true, {@code null} otherwise
*/
abstract protected OUT testFilter(IN nextobj);
/**
* Find the next visualizer.
*/
private void updateNext() {
if(itr == null) {
init();
}
nextobj = null;
while(itr.hasNext()) {
IN v = itr.next();
nextobj = testFilter(v);
if(nextobj != null) {
break;
}
}
}
@Override
public boolean hasNext() {
if(itr == null) {
updateNext();
}
return (nextobj != null);
}
@Override
public OUT next() {
OUT ret = this.nextobj;
updateNext();
return ret;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
}
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