/*
* Copyright 2004-2009 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.util;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.NoSuchElementException;
/**
* Iterator that combines multiple other iterators.
* This implementation maintains a list of iterators which are invoked in sequence until all iterators are exhausted.
* @author Erwin Vervaet
*/
public class CompositeIterator<E> implements Iterator<E> {
private List<Iterator<E>> iterators = new LinkedList<Iterator<E>>();
private boolean inUse = false;
/**
* Create a new composite iterator. Add iterators using the {@link #add(Iterator)} method.
*/
public CompositeIterator() {
}
/**
* Add given iterator to this composite.
*/
public void add(Iterator<E> iterator) {
Assert.state(!inUse, "You can no longer add iterator to a composite iterator that's already in use");
if (iterators.contains(iterator)) {
throw new IllegalArgumentException("You cannot add the same iterator twice");
}
iterators.add(iterator);
}
public boolean hasNext() {
inUse = true;
for (Iterator<Iterator<E>> it = iterators.iterator(); it.hasNext();) {
if (it.next().hasNext()) {
return true;
}
}
return false;
}
public E next() {
inUse = true;
for (Iterator<Iterator<E>> it = iterators.iterator(); it.hasNext();) {
Iterator<E> iterator = it.next();
if (iterator.hasNext()) {
return iterator.next();
}
}
throw new NoSuchElementException("Exhaused all iterators");
}
public void remove() {
throw new UnsupportedOperationException("Remove is not supported");
}
}
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