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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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package org.apache.solr.common.util;
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import java.util.ArrayList;
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import java.util.Iterator;
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import java.util.List;
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/** Chain several Iterators, so that this iterates
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* over all of them in sequence.
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public class IteratorChain<E> implements Iterator<E> {
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private final List<Iterator<E>> iterators = new ArrayList<Iterator<E>>();
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private Iterator<Iterator<E>> itit;
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private Iterator<E> current;
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public void addIterator(Iterator<E> it) {
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if(itit!=null) throw new RuntimeException("all Iterators must be added before calling hasNext()");
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public boolean hasNext() {
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if(itit==null) itit = iterators.iterator();
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return recursiveHasNext();
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/** test if current iterator hasNext(), and if not try the next
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* one in sequence, recursively
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private boolean recursiveHasNext() {
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// return false if we have no more iterators
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boolean result = current.hasNext();
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result = recursiveHasNext();
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/** hasNext() must ALWAYS be called before calling this
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* otherwise it's a bit hard to keep track of what's happening
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throw new RuntimeException("For an IteratorChain, hasNext() MUST be called before calling next()");
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return current.next();
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public void remove() {
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// we just need this class
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// to iterate in readonly mode
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throw new UnsupportedOperationException();