/*******************************************************************************
* Copyright (c) 2008, 2014 Stuart McCulloch
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* Stuart McCulloch - initial API and implementation
*******************************************************************************/
package org.eclipse.sisu.peaberry.cache;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* An {@link Iterator} that iterates over a series of iterators in turn.
*
* @author mcculls@gmail.com (Stuart McCulloch)
*/
final class IteratorChain<T>
implements Iterator<T> {
private final Iterable<T>[] lazyIterables;
private final Iterator<T>[] iterators;
@SuppressWarnings("unchecked")
IteratorChain(final Iterable<T>[] lazyIterables) {
this.lazyIterables = lazyIterables.clone();
iterators = new Iterator[lazyIterables.length];
}
private int index;
public boolean hasNext() {
// peek ahead, but don't disturb current position
for (int i = index; i < iterators.length; i++) {
unroll(i);
if (iterators[i].hasNext()) {
return true;
}
}
return false;
}
public T next() {
// move forwards along the chain
while (index < iterators.length) {
unroll(index);
try {
// is this section finished yet?
return iterators[index].next();
} catch (final NoSuchElementException e) {
index++; // move onto next section
}
}
throw new NoSuchElementException();
}
private void unroll(final int i) {
if (null == iterators[i]) {
iterators[i] = lazyIterables[i].iterator();
}
}
public void remove() {
throw new UnsupportedOperationException();
}
}